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Lonchoptera lutea males produce giant spermatozoa that are more than 2000 μm long and 1.4 μm wide. Unlike the typical brachyceran spermatozoon, they have a highly asymmetrical cross-section with only a single, albeit very large, mitochondrial derivative and a pair of massive accessory bodies, one of which extends throughout the entire length of the sperm tail. The accessory bodies consist of an electron-dense matrix in which numerous peculiar electron-lucid substructures are embedded. In the mated female, the giant spermatozoa are found inside two tubular spermathecae which are also extremely long, measuring 4000 μm or more.

The male reproductive system and sperm ultrastructure of the scorpionfly Furcatopanorpa longihypovalva (Hua & Cai) were investigated using light and transmission electron microscopy. A peculiar feature of the male reproductive system is the position of the epididymis, separately from the base of testis within the peritoneal sheath, unlike the species of other genera of Panorpidae pressed against the lateral base of testis. The mature spermatozoon is filiform, approximately 1600 μm in length. It has largely maintained a mecopteran groundplan condition, with a bilayered acrosome, an elongate nucleus, a neck region, and a long flagellum. As for the sperm features, similarly to other species of Panorpidae, the nucleus has two lateral grooves and a helical appearance. The neck region shows a sheath-shaped centriolar adjunct, beneath the nucleus. The flagellum is helical and consists of a 9 + 2 axoneme, two mitochondrial derivatives of unequal size, one accessory body and two extra-axonemal accessory structures, as in the genus Panorpa of Panorpidae. The uniqueness of spermatozoa of F. longihypovalva lies in the specifically hammer-shaped mitochondrial derivative along most of the flagellum length. The phylogenetic position of the genus Furcatopanorpa in Panorpidae is briefly discussed based on our findings and literature in this respect.

The sperm of Siphonaria algesirae (Gastropoda, Pulmonata), a species with internal fertilization, was studied by light and electron microscopy. The spermatozoon is a very long, uniflagellate cell composed of a conical head with an apical acrosome, a midpiece with a helically coiled external sheath containing a complex mitochondrial derivative with a wavelength of ∼ 5.5 μm, and an endpiece. There are no axonemal microtubules. Instead, nine homogeneous coarse fibers with transverse striations in the apical zone project toward the anterior section of the midpiece. In the posterior zone of the midpiece the coarse fibers are differentiated in a common microtubular axoneme. The complex mitochondrial derivative of the midpiece shows an organized group of 100 A diameter spherical particles. Externally the midpiece is surrounded along its length by a cylinder formed by two membranes. A complex structure separates the transitional zone between the midpiece and the endpiece.

The sperm ultrastructure of the short-faced scorpionfly Panorpodes kuandia- nensis Zhong et al. was investigated using transmission electron microscopy. The spermatozoon is composed of a short head containing a bilayered acrosome and an elongate nucleus, a neck transition region, and a long flagellum. The acrosome consists of an acrosomal vesicle and a central perforatorium. The nucleus has two deep, U-shaped lateral grooves and its chromatin contains a series of parallel, regularly arrayed nuclear fibers. The barrel-shaped centriolar adjunct occupies the most volume of the neck region. The flagellum is helical for its whole length and is formed by an axoneme, two mitochondrial derivatives, a pair of accessory bodies, and peculiar accessory structures. The axoneme has nine accessory microtubules at the ante- rior flagellum region, displaying a 9 19 12 microtubular pattern, but the accessory microtu- bules are short and disappear quickly. The two mitochondrial derivatives differ in length and diameter. In the more posterior region, the remaining anchor-shaped mitochondrial derivative has a circular crystalline region, differing from other mecopteran species. The filiform materi- als are peculiar and lie beside the nucleus and in the flagellum region. Sperm ultrastructural comparison of P. kuandianensis with other families supports a close affinity of Panorpodidae with Panorpidae. In addition, the occurrence of the nine accessory microtubules in the sperm axoneme of Panorpodes indicates that the 9 19 12 axonemal pattern might be a symplesiomor- phy of the Mecoptera. Microsc. Res. Tech. 77:394-400, 2014. V C 2014 Wiley Periodicals, Inc.

In this study, the sperm morphology of the parasitoids Trichospilus diatraeae and Palmistichus elaeisis (Eulophidae) was investigated using light and transmission electron microscopy. In the two species, the sperm are spiral along their entire length and measure about 130 μm and 195 μm in length, respectively. The head region consists of the acrosome and nucleus. The acrosome is composed of an acrosomal vesicle and, in P. elaeisis, a perforatorium. In both species, an extracellular layer in which several filaments are radiated covers the acrosome and the anterior nuclear region. The nuclei are filled with homogeneous and compact chromatin and measure about 50 μm in length in P. elaeisis and 20 μm in T. diatraeae. The flagellum consists of an axoneme with the 9 + 9 + 2 microtubule arrangement spiraled in a long helix, two mitochondrial derivatives coiling around the axoneme and, in P. elaeisis, two accessory bodies. In T. diatraeae were observed transverse striations throughout the central region of the axoneme, whereas the central pair of microtubules was rarely observed. In the final flagellar region in T. diatraeae, different from P. elaeisis, one mitochondrial derivative ends well before the other and both end before the axoneme. The sperm of these two species exhibit features that discriminate one species from each other, as well as characteristics suggest that Eulophidae is closely related to Trichogrammatidae and both of these families are more similar to Eurytomidae than Agaonidae.

The male reproductive system of Mischocyttarus cassununga consists of two testes, each one with three follicles, as occurs in most Vespidae. The seminal vesicle is divided in two chambers, separated by a constriction, so that the anterior locus is a little larger. In the testicular follicles, the spermatozoa are organized in cysts, with approximately 128 per cyst, where the nuclei are oriented toward the follicle center. The spermatozoa of M. cassununga is about 97 μm in length, which makes them the shortest sperm described for Vespidae. Sperm ultrastructure of M. cassununga is very similar of the others Vespidae. But, despite these similarities, the bilobated mitochondrial derivative represents an autapomorphy for M. cassununga. The subdivision of the seminal vesicle has never been observed in any other Vespidae. Thus, this study supports the validity of insect sperm morphology as a tool for phylogenetic analysis within Hymenoptera.

In Digelasinus diversipes, spermatozoa are maintained in bundles, with 74 spermatozoa on average, in the seminal vesicle. These spermatozoa are very short (20 μm) and consist of a head and flagellum. The head includes an acrosome (perforatorium covered by the acrosomal vesicle) and a nucleus. A regular electron-lucent region separates the acrosomal vesicle from the perforatorium, which is inserted parallel to the anterior ending of the nucleus. The small flagellum is composed of two symmetrical mitochondrial derivatives, a centriolar adjunct, an axoneme (9 + 9 + 2), and two accessory bodies. The centriolar adjunct begins above the posterior end of the nucleus and ends covering the anterior tip of two mitochondrial derivatives. In the terminal region of the axoneme, the central microtubules terminate first. The presence of a subacrosomal space, a short mitochondrial derivative diameter, and a short spermatodesm is the ultrastructure characteristics of spermatozoa shared by all “symphyta” species. Differences in the insertion of the perforatorium into the nucleus and the position of the centriolar adjunct distinguish Dielocerinae and the Arginae studied previously. The number of spermatozoa per cyst is variable. Furthermore, additional characteristics that had not been described for “symphyta” were also found, such as the number of follicles per testis. Microsc. Res. Tech., 2012. © 2011 Wiley Periodicals, Inc.

Sperm morphology of orthalicid gastropods Clessinia pagoda, Spixia tucumanensis, Plagiodontes daedaleus (Odontostominae) and Drymaeus hygrohylaeus, D. poecilus, Bostryx stelzneri (Bulimulinae) are examined and described for the first time using transmission electron microscopy. Spermatozoa show the general characteristic of Pulmonata: an acrosomal vesicle, sperm nucleus helical, mitochondrial derivative forming a continuous sheath with paracrystalline material and coarse fibers associated with axonemal doublets. Features in the acrosomal complex and shape of the nucleus distinguish orthalicid sperms from other stylommatophoran. The acrosomal pedestal is traversed by fine striations in all species examined except in S. tucumanensis. The structure and thickness of the perinuclear sheath with a single or double layer of electron-dense material ensheathing the nuclear apex is characteristic of the group. The presence of a subnuclear ring in Drymaeus, Bostryx and Clessinia species is also reported. A data matrix of eleven species per 34 characters (16 sperm plus 18 anatomical and shell characters) from orthalicids plus other stylommatophoran and systellommatophoran representative species was constructed. Three cladistic analyses (sperm-based, anatomical-based and a combined sperm + anatomical-based) were performed to test the phylogenetic potential of sperm ultrastructure in orthalicid systematics and understand how sperm characters affect the topology and resolution of the obtained trees. Stylommatophora resulted in a monophyletic clade in the sperm-based and in the combined-character analysis. Orthalicidae is monophyletic only in the combined-character cladogram. Within Orthalicidae, Odontostominae is recovered as a monophyletic clade in all analyses, while Bulimulinae is paraphyletic in all trees except in the combined phylogeny. The present study and cladistic analyses performed support the hypothesis that characters on sperm ultrastructure are informative for stylommatophoran systematic and phylogenetic approaches, providing synapomorphies at familiar, subfamiliar and generic level. Fil: Cuezzo, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo; Argentina

The ultrastructure of the spermatozoa of Trypoxylon (Trypargilum) albitarse is described here for the first time within this genus. Testes and seminal vesicles were dissected and processed for transmission electron microscopy. In the testicular follicles, the spermatids are arranged in a maximum number of 32 for each cyst. The spermatozoa are slender and they measure approximately 150 μm in length. The head is about 17 μm long and is formed by the acrosome and the nucleus. The flagellum consists in an axoneme, two mitochondrial derivatives, two accessory bodies and, at the nucleus–flagellum transition, a symmetric centriolar adjunct. The axoneme presents the typical 9 + 9 + 2 microtubule pattern. In the terminal region, the central microtubules and nine doublets finish first, followed by the accessory microtubules. Both mitochondrial derivatives begin together and are inserted in the base of the centriolar adjunct. Along the middle region, the larger derivative has almost twice the area of the smaller one and includes a discrete paracrystalline region. At the tip, the smaller derivative ends before the larger one and both before the axoneme. The characters derived from the ultrastructure of the spermatozoa of T. albitarse show synapomorphies shared with the Apoidea and present characters that are probably apomorphic for the Crabroninae subfamily.

This study represents the first sperm description of a Vespinae species (Vespa crabro). The acrosome consists of an acrosomal vesicle and a perforatorium. The nucleus has compact chromatin and shows lenticular structures on the nuclear envelope. These structures, which have never been observed in a hymenopteran sperm, could be clusters of nuclear pores. The centriolar adjunct has an asymmetric pattern and shows a structured periphery. The centriole consists of 9 accessory microtubules and 9 doublet microtubules devoid of arms and spokes. The axoneme has a 9 + 9 + 2 microtubule pattern and the accessory microtubules have 16 protofilaments. The mitochondrial derivatives differ in length and diameter. The larger one is adjacent to the nuclear base, while the smaller one begins below the centriolar adjunct. They possess three distinct areas and a large paracrystalline region, which occurs only in the large one. The large mitochondrial derivative ends first, followed by the small one. The axoneme gradually disorganizes: first the central microtubules disappear, then the doublets, which show opened B-tubules, and finally the accessory microtubules. The sperm morphology of V. crabro is very similar to that of the polistine wasp, Agelaia vicina. This can indicate that, in Vespidae, sperm morphology is maintained without important variations among subfamilies and/or that this similarity indicates close phylogenetic relationship between these two subfamilies. Although Vespidae phylogenetically related to Formicidae, these data suggest that the former more closely related to Apoidea than to Formicidae.

The "zipper line" of Drosophila melanogaster and of Drosophila species characterized by giant spermatozoa (D. hydei, D. kanekoi and D. bifurca) was studied by electron microscopy using conventional thin-sections, lectin labeling and freeze-fracture replicas. In cross sections the membrane specializations are located either at the level of the short cistern close to the large mitochondrial derivative where a small tuft of glycocalyx is visible or, in species characterized by long spermatozoa, along a cistern beneath the plasma membrane. In correspondence of such cistern, the plasma membrane exhibits a thick and extended glycocalyx. At this level, as well as at the short tuft of D. melanogaster, alpha-mannose residues were detected. The "zipper" of D. melanogaster consists of rows of intramembrane particles longitudinally disposed along the sperm tail and associated with the external face of the plasma membrane. On the protoplasmatic face a narrow ribbon of transversal grooves is visible. Freeze-fracture replicas have revealed, in the region characterized by extended glycocalyx, the presence of a large ribbon of intramembrane particles disposed in parallel transversal rows, associated with the protoplasmatic membrane face. On the complementary external face a ribbon of parallel transversal grooves was observed. It is suggested that membrane specializations are mechanical devices to protect spermatozoa from torsion and bending in the seminal vesicles and then in the female storage organ.

The sperm ultrastructure of a few species of Limoniidae (Limonia nigropunctata; L. nubeculosa; Chionea n. sp.; C. alpina; C. lutescens) was studied. The two species of Limonia have a monolayered acrosome with crystallized material, a three-lobed nucleus in cross section, a ring of centriole adjunct material and a flagellum which consists of a 9 + 9 + 1 axoneme and a single mitochondrial derivative. The central axonemal tubule is provided with 15 protofilaments in its tubular wall, while the accessory tubules have 13 protofilaments and are flanked by the electron-dense intertubular material. The three species of Chionea share a monolayered acrosome, a nucleus with two longitudinal grooves, a centriole adjunct material which surrounds the centriole and the initial part of the axoneme. The axoneme is of conventional type, with 9 + 9 + 2 microtubular pattern, with accessory tubules provided with 13 protofilaments and intertubular material. However, in C. lutescens the accessory tubules start with 15 protofilaments and transform into a tubule with 13 protofilaments. These data are discussed in the light of the phylogenetic relationship between Limoniidae and Tipulidae. For this purpose, the sperm ultrastructure of Nephrotoma appendiculata was also considered comparatively.

The spermatozoa of Diasemopsis comoroensis and Diasemopsis meigenii differ from the conventional brachyceran type in several respects. Not only are they very long but they are also extraordinarily wide, especially at the very end of the tail. The latter is effected by two cellular components: oversized mitochondrial derivatives and a prominent central band, which is a peculiar structure not known from any other spermatozoa. Based on its position with respect to the other organelles and its origin during early spermiogenesis, the central band is interpreted as a derivative of the centriolar adjunct material. Like the axoneme, the mitochondrial derivatives and the central band extend through the entire length of the spermatozoon tail. The spermatozoon tail is helical and can be coiled up into a tight cone-shaped spiral with a peculiar corkscrew shaped end portion. The potential adaptive significance of these features and their coevolution with the morphology of the female's multi-chambered ventral receptacle are discussed, as are sperm competition and cryptic female choice.

The present research represents the first description of a Vespidae species spermatozoon. In Agelaia vicina, the sperm head is composed of an acrosome and a nucleus. The acrosome consists of an acrosomal vesicle, oval shaped in cross sections, and a perforatorium, that projects into the anterior nuclear region. The nucleus is elongated and oval shaped in cross sections. The nucleus-flagellum transition region includes the centriolar adjunct, the nucleus base and the anterior portions of the axoneme and of the large mitochondrial derivative. The centriolar adjunct begins as a thin layer between the nucleus and the large mitochondrial derivative, while just below it acquires a lateral extension partially surrounding the large mitochondrial derivative. In its medial portion, it is triangular shaped, situated laterally to the axoneme and the large mitochondrial derivative, and it finishes in contact with the tip of the small mitochondrial derivative. The flagellum is composed of a 9 + 9 + 2 axoneme, two mitochondrial derivatives and two accessory bodies. The large mitochondrial derivative begins laterally to the nuclear base, and the small one below the centriolar adjunct. Only the large mitochondrial derivative presents a paracrystalline core, situated distally in relation to the axoneme. In the posterior flagellar region, the small mitochondrial derivative finishes first, followed by the large one and both accessory bodies. Although Vespidae belong to the superfamily Vespoidea, as Formicidae, the sperm ultrastructure of A. vicina is phylogenetically more closely related to Apoidea, and curiously very different from that observed for ants. This study supports the use of insect sperm morphology as a tool for phylogenetic analysis, especially in the Hymenoptera order.

The intertidal polychaete species Stygocapitella subterranea (Parergodrilidae) is characterised by extraordinary biology and morphology, resembling those of clitellates and Hrabeiella periglandulata, a terrestrial species of Annelida. An ultrastructural study of the spermatogenesis and spermatozoa was undertaken to elucidate whether these similarities might exhibit adaptive characters typical of annelids with highly derived reproductive modes. A second goal was to find out whether there are some common apomorphic features between S. subterranea and its sister taxon, Parergodrilus heideri, instead of the differences observed on the light-microscopic level, as well as to look for potential synapomorphies to support a suggested relationship to Orbiniidae and Questidae. Spermatogenesis conforms to the general pattern typical of Annelida. Spermatids develop on large cytophores comprising at least 128 cells. The spermatozoa are extremely thread-like and, with a length of about 320 μm, are among the longest spermatozoa known for annelids. The acrosome is elongated and consists only of an acrosomal vesicle with a large subacrosomal space. A conspicuous feature is the incomplete chromatin condensation, resembling late spermatids. In the long midpiece, there is a single ring-shaped mitochondrial derivative, which develops by fusion out of a multiple array of eight mitochondria surrounding the axoneme. There is a distinct annulus between midpiece and tail. The proximal part of the tail is immobile; the axoneme is surrounded by a thick layer of cytoplasm and bears a velum-like extension. In addition to characters apomorphic for S. subterranea, these latter three features exhibit certain similarities to P. heideri that are likely to be synapomorphic. Unfortunately, a relationship of Parergodrilidae to an orbiniid/questid clade does not receive additional support from spermatozoal characters. Similarities with either Clitellata or H. periglandulata are likely to be primarily related to corresponding features of their reproductive biology rather than to phylogenetic relationship.

Euglossine spermatozoa are the longest described to date for the Hymenoptera. This cell includes a head and a flagellar region. In transverse sections, the acrosome is circular at the tip but has an oval contour along most of its length. The perforatorium penetrates into a deep cavity in the nuclear tip. The flagellum consists in an axoneme, a pair of mitochondrial derivatives, a centriolar adjunct and a pair of accessory bodies. The axoneme has a 9+9+2 microtubule pattern which becomes gradually disorganized in the final portion, with the central microtubules and the nine doublets terminating simultaneously, followed by the accessory microtubules. The mitochondrial derivatives are asymmetric both in length and diameter. Sectioned transversally, the derivatives are ellipsoidal or have a pear shape. The larger one has a more obvious paracrystalline region. The centriolar adjunct begins at the nuclear base and extends parallel to the axoneme until it encounters the smaller mitochondrial derivative, on which it fits, making a concave groove. In addition to these consistent euglossine features, species-specific differences that might be useful in phylogenetic work on the group are also noted.

Sperm ultrastructure is described for the nudibranch gastropod Cadlinella ornatissima, type species of the genus Cadlinella (Thiele). Although C. ornatissima exhibits most of the sperm features characteristic of other Opisthobranchia and the Pulmonata (a small, rounded acrosomal vesicle, a complex, helical, mitochondrial derivative - partially paracrystalline, coarse fibres associated with the axoneme), it also possesses a number of previously undescribed and possibly unique features (a longitudinally inrolled acrosomal pedestal, an axial structure within the cavity of the acrosomal pedestal, an electron-dense collar at the anterior region of the acrosomal pedestal, the presence of crystalloid bodies within the glycogen helices of the mitochondrial derivative). To our knowledge this is the first report of crystalloid bodies in mature sperm of any mollusc. Collectively this evidence raises questions concerning the affinities and systematic position of Cadlinella within the Nudibranchia. The peculiar nature of the sperm differences, in comparison with other investigated nudibranchs, suggest that Cadlinella is not easily linked to either the Cadlinidae or Chromodorididae, and should be considered incertae sedis.

The spermatozoon of Atelura formicaria (Zygentoma) shows several features that are typical of insects: an apical acrosome, an elongated dense nucleus, a centriole with expanded centriolar adjunct material, two large mitochondrial derivatives, and two thin accessory bodies located beneath the nucleus. The axoneme exhibits a 9 + 9 + 2 pattern with accessory tubules formed by 16 protofilaments and intertubular material. However, spermatozoa of A. formicaria show some remarkable features. The sperm cell is short for an insect, being only 50 µm in length. The nucleus is characterized by the presence of two lateral grooves which are filled with numerous infoldings of the nuclear envelope. In a cross-section the chromatin has the configuration of the Leonardo da Vinci’s ‘Vitruvian man’. Each mitochondrial derivative has a peculiar structure with peripheral cristae and four crystalline bodies in its matrix; two of these crystalline bodies are large and have differently orientated cristal planes. At the end of spermiogenesis, sperm bundles are stored in the proximal part of the testes. Secretions from the epithelial wall of this region give rise to large globular structures. These include sperm bundles intermingled with dense granules, forming the so called ‘spermatolophids’. These formations descend along the deferent duct and are stored in the expanded seminal vesicle. Atelura spermatozoa do not pair as in some Lepismatidae, nor do they fuse as in Tricholepidion (Lepidotrichidae). Thus, sperm aggregation in Zygentoma is realized according to different modalities and can hardly be considered as a synapomorphic trait of its subtaxa.

To verify the questionable description of sperm structure of Trichogramma dendrolimi, in relation to Chalcidoids, a reinvestigation was undertaken. The spermatozoa appear wavy along their entire length. A small acrosome, together with the anterior nuclear region, is surrounded by an extracellular sheath, from which filaments radiate. The nucleus is helicoidal and attached to the flagellum by a centriolar adjunct. The axoneme has the 9 + 9 + 2 microtubule arrangement pitched in a long helix, with the spiralling mitochondrial derivatives coiling around it. Therefore, the spermatozoa of T. dendrolimi are very similar to those of other chalcidoids and different from the first description. It is now possible to affirm that the helical sperm structures are an apomorphic homology for Trichogrammatidae as well as Eulophidae, Pteromalidae, Eurytomidae, Torymidae, Mymaridae and for some other chalcidoids, if not all.

In the present study, spermatozoon ultrastructure was documented in two species of hangingflies, Bittacus strigosus Hagen (Mecoptera: Bittacidae) and B. stigmaterus Say. Structures considered important to phylogenetic assessment that were observed in B. strigosus and B. stigmaterus included a short bilayered acrosome, elongated nucleus, tube-like glycocalyx, centriole adjunct material, accessory bodies, two mitochondrial derivatives, extra axonemal rods, globular units, and 9+2 arrangement of microtubules in the axoneme. Comparisons were made to Bittacus planus Cheng, which was previously examined by electron microscopy ( Xie and Hua 2010 ). Similarities among the ultrastructural characteristics of the three Bittacus species support the monophyly of this genus. Displacement of a mitochondrial derivative by an accessory body was documented for the first time. This paper includes clarifications on differences between accessory bodies and extra axonemal rods, which are issues important to phylogenetic placement.

Summary Sperm ultrastructure and the number of sperm per bundle were studied in two Drosophila species from the tripunctata radiation, D. dunni and D. cardini. The number of sperm per bundle in both species was found to have an unusual frequency distribution, as none of the bundles obeyed the 4(2”) rule proposed for species with definitive spermatogonia division. The absolute and relative size of the cross sectional areas of the mitochondrial derivatives of D. dunni and D. cardini sperm was found to be somewhat different from D. hydei (repleta radiation), and very different from D. melanogaster of the Sophophora radiation. Lastly, a mass of residual material and a desmosome-like attachment plaque were demonstrated between the axoneme and the large mitochondrial derivative in D. dunni and D. cardini sperm. This study highlights the importance of ultrastructural studies of spermatogenesis in the analysis of the phylogeny of Drosophila.

The spermatozoa of Bephratelloides pomorum are very long and fine. Each spermatozoon measures about 620 μm in length by 0.38 μm in diameter and, when seen under the light microscope, appears to be wavy along its entire length. The head, which is approximately 105 μm, comprises a small acrosome and a nucleus. The acrosome is made up of a cone-shaped acrosomal vesicle surrounding the perforatorium and the anterior end of the nucleus. Innumerable filaments radiate from it. The perforatorium has a diameter equal to that of the nucleus at their junction, where it fits with a concave base onto the rounded nuclear tip. The nucleus is helicoidal and completely filled with homogeneous compact chromatin. It is attached to the tail by a very long and quite electron-dense centriolar adjunct that extends anteriorly from the centriole in a spiral around the nucleus for approximately 8.5 μm. The tail consists of an axoneme with the 9+9+2 microtubule arrangement pitched in a long helix, as well as a pair of spiraling mitochondrial derivatives (with regularly arranged cristae) that coil around the axoneme, and two small accessory bodies. As well as the spiraling of the nucleus, mitochondrial derivatives and axonemal microtubules, the sperm of B. pomorum present other very different morphological features. These features include the acrosome and centriolar adjunct, both of which differentiate the spermatozoa from the majority of sperm found in other Hymenoptera. In addition these structural variations demonstrate that the sperm of chalcidoids provide characteristics that can certainly prove useful for future phylogenetic analysis at the subfamily level and, possibly, the genus too.

Results from a transmission electron microscope study of the spermiogenesis and spermatozoon of Meara stichopi (Nemertodermatida, Platyhelminthes) indicate that the sperm type of the Nemertodermatida has evolved from the primitive metazoan sperm type rather than from an aberrant biflagellar sperm type as found in many other flatworms. The spirally coiled mitochondrial derivative in the mature spermatozoon develops from two large oval mitochondria in the early spermatid stages. A single flagellum grows out from a peripheral basal body adjacent to a perpendicularly placed accessory centriole. The basal body moves to a distal depression of the nucleus, and becomes equipped with an anchoring fibre apparatus. Most of the flagellum becomes axially incorporated into the developing spermatid. No trace of a second flagellum was found in any stage of the spermiogenesis. Rounded vesicles appear around the proximal, tapering end of the elongating nucleus. Most probably these vesicles form a thin acrosomal structure in the mature spermatozoon. No dense bodies, characteristic of many other ‘turbellarian’ flatworm sperm types, were found.

The spermatogenesis of Allostoma sp. and the organization of mature spermatozoa are described by means of transmission electron microscopy. All stages of sperm development were observed in mature testes, which are bordered by a layer of fibrous connective tissue. The primary spermatogonium produces 64 spermatids, grouped as a cytophore. The process of spermiogenesis occurs at the periphery of the cytophore, when the sperm body is formed and released at complete maturation. The mature spermatozoon is a flattened, filiform structure. It is aciliary. Its anterior end is not distinguishable from the posterior one in the testis. The nucleus, showing an approximately rectangular cross section, is situated centrally and the chromatin is densely packed. A membranous cylinder, located on each side of the nucleus, contains conspicuous stacks of clear thick-envelope vesicles, and a long mitochondrial derivative placed peripherally. The vesicles show contacts with the cylinder membrane and the outer sperm membrane. Their supposed Golgi-derived content may thus be released into the external medium. A hypothesis is proposed about the role of these vesicles in sperm motility.

The ultrastructure of spermiogenesis and spermatozoa is examined for the first time in the heterogastropod family Mathildidae (Mathilda brevicula Bavay and Mathilda sp.). Mathildid spermatozoa exhibit the following features: (1) an ovoid acrosomal vesicle showing curved dense layers basally and underlain by a thin curved plate; (2) a solid, rod-shaped nucleus showing a shallow basal invagination (nucleus helically keeled in Mathilda sp.); (3) a midpiece composed of a 9+2 axoneme, 9 thick and periodically banded coarse fibres (associated with the axonemal doublets) and a continuous mitochondrial derivative; (5) glyco-gen piece composed of the axoneme surrounded by dense granules; (6) and end piece (paddle-shaped terminally). Results of the study demonstrate that mathildids share the same key sperm and spermi-ogenic features observed in the Architectonicidae. The monophyly of the Architectonicoidea, established by previous authors on anatomical grounds, is therefore confirmed using sperm morphology. Spermatozoa of the two mathildids investigated lack the periodically banded midpiece structures seen in investigated species of Architectonica (A. pcrspectiva (Linnaeus), A. perdix (Hinds)), Heliacus (H. (Heliacus) variegatus (Gmelin)) and Pseudotorinia (P. laseronorum (Iredale)) thereby resembling most closely the spermatozoaof Philippia lutea (Lamarck) and Psilaxis oxytropis (A. Adams) which also lack suchbanded structures. Given the widely accepted primitive status of the Mathildidae within the Architectonicoidea, the genera Philippia and Psilaxis may prove to be relatively basal rather than advanced genera within the Architectonicidae. Thi: view needs to be tested by examination of sperm morphology in other genera of the Architectonicidae and also the basal mathildid genus Tuba sensu lato (= Gegania + Tubena). Such information will be vital in any future cladistic study of the Architectonicoidea.

In this study, the morphology of spermatozoa of Bethylidae Dissomphalus connubialis (Pristocerinae) was analyzed using light and transmission electron microscopy. Spermatozoa of this species are thin, measure approximately 130 μm in length and comprise a head region and flagellum region. The head is formed by the acrosome and nucleus. The acrosome consists of the acrosome vesicle and the perforatorium, the posterior portion of which is inserted into a cavity at the anterior extremity of the nucleus. The nucleus is compact, electron-dense and measures 15 μm in length. The flagellum possesses two mitochondrial derivatives, two accessory bodies and one axoneme with a 9+9+2 microtubular pattern. The nucleus is connected to the flagellum by the centriole adjunct. Mitochondrial derivatives are compact, apparently without paracrystalline material and with rare mitochondrial cristae. They are asymmetric in length, such that the larger mitochondrial derivative begins parallel to the posterior region of the nucleus and the smaller mitochondrial derivative begins just below the centriole adjunct. The basic structure of spermatozoa of D. connubialis is similar to that of other Aculeata studied. However, this species shows characteristics not seen in other Hymenoptera, such as the wide electron-lucid region that separates the acrosomal vesicle from the perforatorium and the depth of the cavity in the anterior extremity of the nucleus, into which the base of the perforatorium is inserted. There are also characteristics that distinguish this species from Bethylidae Prorops nasuta, including the fact that one of the mitochondrial derivatives lies to parallel to the nucleus over a long distance, the small quantity of cristae, the absence of paracrystalline material in these organelles, and the fact that the accessory microtubules are the first to terminate in the final portion of the flagellum.

Spermatozoa of the triatomideo Rhodnius prolixus possess an axoneme with a 9 + 9 + 2 microtubule pattern and two mitochondrial derivatives. Bridges occur between axoneme and mitochondrial derivatives. Two paracrystalline structures embedded in amorphous regions were observed in the mitochondrial derivative. The use of the negative staining technique shows a zig-zag profile in the mitochondrial derivatives due to infolding to the cristae, regularly spaced with approximately 50 nm. This spacing is also observed in the distribution of the strands of particles in the mitochondrial membrana as seen in freeze-fracture replicas. In the P-fracture face of the flagellar plasma membrane, a regular array of the intramembranous particles was observed. This array consists of two rows, with 12-15 particles, and occurs in the space between the mitochondrial derivatives. Thus R. prolixus spermatozoon present a membrane domain, localized in the flagellar region, and bridges between mitochondrial membrane derivatives and the plasma membrane are probably attached to the flagellar components. These membrane specializations may be related to the production of co-ordinated flagellar movement, and can contribute significantly to further phylogenetic studies.

The ultrastructure of ejaculated sperm of the honey bee, Apis mellifera L., was studied after sperm were processed by using a high-pressure freezing fixation and freezing substitution method. The electron micrographs of samples processed by this method clearly revealed previously unobserved or unresolved fine details, particularly those in the acrosomal complex. The present study demonstrates that the acrosomal complex of honey bee sperm consists of an anterior tubular acicular apex, an enlarged spherical region, and the elongated acrosomal proper. Internally, the structures of acrosomal complex confirm the general description of the tri-layer model; having an extra-acrosomal layer, an acrosome vesicle, and a central acrosomal rod located in a subacrosomal cavity. The acrosomal rod terminates anteriorly with an electron dense corpuscle in an ensheathing cap at the spherical region. The electron micrographs also show the presence of a centriolar adjunct and a structure possibly of a centriolar or basal body origin. The chemical and functional aspects of these ultrastructures remain unknown.

Spermatozoa of Sergentomyia minuta were examined by light, scanning, and transmission electron microscopy. They were seen to be formed by a head and a tail. The head was characterized by an acrosomal complex with a thin space containing granular material organized as in a perforatorium. The tail contained a “9 + 9 + 0”; axoneme and one mitochondrial derivative. A comparison with the spermatozoon ultrastructure of other Diptera, particularly Psychodidae, is discussed.

Sperm ultrastructure is described for Pleurehdera haraldi Er. & Ev. Marcus, 1970 and contrasted with data from previously investigated members of the Notaspidea. The acrosomal vesicle is small (length 0.13 pm, breadth 0.09 pm) and supported basally by a short (0.37 pm) pedestal which overlaps extensively with the tapered nuclear apex. Nuclei are approxi-mately 15 pm long and sometimes exhibit a single helical keel. Absence of the keel in many of the observed spermatozoa suggests possible dimorphism with regard to this feature. A short basal invagination of the nucleus forms the point of attachment for the centriolar derivative and axoneme/coarse fibre com-plex. A single glycogen-filled helix is present within the mitochondrial derivative of the midpiece. Distally, an annulus occurs at the junction of the elongate (at least 160 pm) midpiece and short (1.5 pm) glycogen piece. Axonemal microtubules persist to the posterior tip of the spermatozoon. Comparison with other Notaspidea confirms that Pleurehdera is closest to Berthella and Berthellina within the Pleurobranchinae (of the family Pleurobranchidae). Sperm morphology supports the unity of the pleurobranchine tribe Berth- ellini.

In the seminal vesicle of the ‘symphyta’ Arge pagana the spermatozoa are stored in motile spermatodesm bundles, maintained by an anterior cap of extracellular material. This cap consists of a denser cortex and of an internal matrix, where part of the sperm heads are embedded. The number of spermatozoa per bundle is variable. The spermatozoa are short, only 30 μm long, with a head region of about 23 μm, and a very short flagellum of about 7 μm. The head includes the acrosome, with a perforatorium, and the nucleus. The flagellum consists of an axoneme, with a 9 + 9 + 2 microtubule pattern, a centriolar adjunct, two mitochondrial derivatives and two accessory bodies. The mitochondrial derivatives are very slender and of different lengths. The longer begins at the base of the nucleus, while the shorter one starts just below the base of the centriolar adjunct. This latter is asymmetric and appears at the nuclear base, extending parallel to the axoneme up to the anterior end of the smaller mitochondrial derivative. The short spermatodesmata and the small mitochondrial derivatives characterize the A. pagana sperm. In addition, the centriolar adjunct asymmetry and the occurrence of spermatodesm bundles might be considered plesiomorphic states present in the basal Tenthredinoidea.

Comparative sperm ultrastructure within the molluscan nudibranch genus Halgerda (Discodorididae) was examined for the first time using transmission electron microscopy (TEM), based on 17 of the 35 known species. In addition, observations on two other discodorids are made to facilitate outgroup comparison with Halgerda, including one species of Discodoris (D. boholiensis) and Asteronotus cespitosus (currently accepted as the closest sister taxon to Halgerda). Comparison was also made with some genera of the Chromodorididae in view of sperm similarities. Spermatozoa of all species examined were of the complex, helical, elongate ( approximately 300-400 micro m) type characteristic of most heterobranch gastropods. These cells exhibit the following discrete regions (in anteroposterior sequence) : an acrosomal complex (composed of a rounded, membrane-bound vesicle and a column-like pedestal); a solid, helical nucleus; an elongate, helical midpiece (composed of an axoneme and associated nine coarse fibers, an enveloping mitochondrial derivative of matrix, and paracrystalline materials and glycogen helix); an annular complex; and a short glycogen piece. Of these regions, the midpiece is by far the longest, occupying over 90% of the total sperm length. Comparison with other members of the radula-bearing cryptobranch dorids reveals several sperm similarities to other genera in the clade, particularly those of other Discodorididae and also with the Chromodorididae. Comparison with previously studied genera reveals noteworthy sperm differences within the Discodorididae. The most notable differences are the internal structure of the acrosomal pedestal (long and homogeneous in Halgerda, Discodoris; short and homogeneous in Asteronotus; long and finely striated in Rostanga; oblong with angular electron-lucent striations in Jorunna) and the internal structure of the glycogen piece. The pronounced helical keels of most Halgerda and Discodoris nuclei contrast with the weakly helical nucleus of Asteronotus. Sperm features alone do not provide a means of defining the genus Halgerda or the family Discodorididae nor do they support the monophyletic status of the caryophyllidia-bearing dorids. Important sperm characters such as the acrosome, nucleus, and midpiece can often still be determined from specimens that have been initially fixed in formalin, then stored in ethanol for extended periods of time (i.e., museum material). Of all sperm features, the mitochondrial derivative of the midpiece is the most resistant to long-term fixation : the survival of acrosomal, nuclear, and axonemal components is variable, presumably a factor of prefixation autolysis, varied primary fixation times and temperatures, formalin quality, and duration of alcohol storage.

Sperm ultrastructure has been studied in three species of the taxa Mecoptera and Siphonaptera. The spermatozoon of the scorpion fly Panorpa germanica shows an apical bilayered acrosome, a helicoidal nucleus, a centriolar region and a 9+2 flagellar axoneme helicoidally arranged around a long mitochondrial derivative. A second mitochondrial derivative is very short and present only in the centriolar region. A single accessory body is present and it is clearly formed as a prolongation of the centriole adjunct material. Two lateral lamellae run parallel to the nucleus. The snow fly Boreus hyemalis has a conventional sperm structure and shows a bilayered acrosome, a long nucleus, a centriolar region, two mitochondrial derivatives and two accessory bodies. The axoneme is of the 9+2 type and is flattened at the tail tip. Both P. germanica and B. hyemalis have two longitudinal extra-axonemal rods and have a glycocalyx consisting of longitudinal parallel ridges or filaments. The spermatozoon of the flea Ctenocephalides canis has a long apical bilayered acrosome, a nucleus, a centriolar region, a 9+2 axoneme wound around two unequally sized mitochondrial derivatives, and two triangular accessory bodies. In the posterior tail end the flagellar axoneme disorganises and a few microtubular doublets run helicoidally around the remnant mitochondrial derivative. The glycocalyx consists of fine transverse striations. In all three species, the posterior tail tip is characterised by a dense matrix embedding the disorganised axoneme. From this comparative analysis of the sperm structure it is concluded that Mecoptera, as traditionally defined, is monophyletic and that B. hyemalis is a member of Mecoptera rather than of Siphonaptera.

Sperm ultrastructure is examined in representatives of five genera of the nudibranch gastropod family Chromodorididae: (Chromodoris, Hypselodoris, Glossodoris, Risbecia and Pectenodoris) and the results compared with previous work on other gastropods, especially other nudibranchs. As chromodoridid phylogeny is still incompletely understood, this study partly focuses on the search for new and as yet untapped sources of informative characters. Like spermatozoa of most other heterobranch gastropods, those of the Chromodorididae are elongate, complex cells composed of an acrosomal complex (small, rounded acrosomal vesicle, and columnar acrosomal pedestal), a condensed nucleus, sub-nuclear ring, a highly modified mid-piece (axoneme + coarse fibres surrounded by a glycogen-containing, helically-coiled mitochondrial derivative) and terminally a glycogen piece (or homologue thereof). The finely striated acrosomal pedestal is a synapomorphy of all genera examined here, but interestingly also occurs in at least one dorid (Rostanga arbutus). Substantial and potentially taxonomically informative differences were also observed between genera in the morphology of the nucleus, the neck region of the mid-piece, and also the terminal glycogen piece. The subnuclear ring is shown for the first time to be a segmented, rather than a continuous structure; similarly, the annular complex is shown to consist of two structures, the annulus proper and the herein-termed annular accessory body.

The spermatozoa of Solenopsis invicta are long and slender, measuring about 70 μm in length, of which the head region measures approximately 13 μm. The head consists of an acrosome formed by an acrosomal vesicle covering a perforatorium and a nucleus. This latter measures about 12 μm, has compact chromatin, and many translucent areas. The flagellum consists of an axoneme of 9+9+2 microtubules that begins just below the nuclear base. The two mitochondrial derivatives are of almost equal diameter, and there are two accessory bodies. The nucleus is attached to the flagellum by a centriolar adjunct located between the baso-lateral region of the nucleus and the anterior mitochondrial derivative extremities. Therefore, the nucleus–flagellum transition region of the spermatozoa of S. invicta is very similar to that of other ants and differs from the first description of this species [Ann. Entomol. Soc. Am. 67 (1967) 632]. In relation to other aculeates, it is possible that three characteristics (type of centriolar adjunct, presence of paracrystalline areas in each mitochondrial derivative, and the position of these areas within each derivative) may be autopomorphies for the Formicidae.

The flagellum of Apis mellifera (Hymenoptera, Apidae) consists of two mitochondrial derivatives, an axoneme and two accessory bodies. The mitochondrial derivatives are of unequal size and lie parallel to the axoneme. In the larger derivative four regions can be distinguished while in the smaller, only three. The region occurring only in the larger derivative consists of paracystalline material. The smaller mitochondrial derivative terminates anterior to the larger one. An extremely long centriolar adjunct is observed between the nucleus and the smaller mitochondrial derivative. This adjunct is compact, very electron dense and gradually tapers from base toward apex, finishing at the anterior extremity of the axonemal microtubules. In this flagellar region, there is only one accessory body present between the larger mitochondrial derivative and the axoneme. Anteriorly, the tips of the axonemal microtubules are inserted in a well developed mass of granular appearance. This material surrounds the nuclear base, separating it from the anterior end of the larger mitochondrial derivative. We believe that the structure identified here as a centriolar adjunct is homologous to that observed in Formicidae, Ichneumonoidea and Symphyta. Therefore, very probably, it is common to most Hymenoptera.

The spermatozoon of Onchidella celtica shows many peculiar features. The acrosome is formed by an apical vesicle and a pedestal consisting of a principal body which is flanked by two electron-dense elliptical elements. The mitochondrial derivative consists of three different components: peripheral layers of paracrystalline material, concentric cisterns, and two cylindrical compartments. The 9 + 9 + 2 axoneme shows 9 small deposits of glycogen granules in correspondence with the axonemal “spokeheads,” and a small assembly of possibly proteic material lying close to the two central tubules. Another intraaxonemal deposit of glycogen granules is present at the level of the “glycogen piece.” Most of the observed features are in substantial agreement with those of another species of the Onchidiidae. This confirms the constancy of sperm structure among the members of a single family of the Gastropoda.

The ultrastructure of the mature sperm of the mayfly, Dolania americana Edmunds and Traver (Ephemeroptera : Behningiidae), is described from scanning and transmission electron microscopy. The head is 0.7–1 μm wide and 4.6–6.9 μm long, rodlike, and topped by a short, rounded acrosome 0.4 μm long and 0.6 μm wide. The flagellum is 5–6 times the head length and is flattened, except for a thin, tubelike terminal portion. The axoneme pattern is 9-9-1 (9 outer singlet microtubules, 9 doublet microtubules, and a central dark element) and is new for Ephemeroptera. The inner dynein arms are conspicuous and outer arms are lacking, and radial spokes and a central sheath are prominent. A densely-staining and bi-lobed accessory body lies adjacent to the axoneme. A mitochondrial derivative with regularly arranged transverse-to-oblique cristae lies adjacent to the accessory body.

Spermiogenesis of Anthonomus grandis Boheman, the cotton boll weevil, was studied by transmission electron microscopy. The basic morphologic features investigated and illustrated were: acrosome, nucleus, fibrous masses, microtubules, and mitochondrial derivatives. A centriole adjunct was observed to surround the basal body (centriole derivative) early in spermiogenesis, but it subsequently disappeared. In the sperm tail, one mitochondrial derivative developed into a rod-like structure that inserted into a concavity at the base of the nucleus and terminated near the end of the tail. This mitochondrial derivative may provide a rigid base for the undulating membrane. In addition, the attachment of the rod to the nucleus may serve in a manner analogous to the function that has been suggested for the centriole adjunct: it may anchor the head to the tail. A possible abnormal condition may arise when the mitochondrial derivative rod fails to insert into the sperm nucleus.

To provide a basis for subsequent studies of the effect of X-rays on Dermestes frischii (Coleoptera : Dermestidae), the ultrastructure of the somatic and germ cells of the testes of this species is described. The somatic cells are of 3 types, the apical, cyst wall, and follicle wall cells. The follicle wall consists of a single continuous layer of epithelial cells lying on a basal lamina, which in the germarium is subdivided and contains a discontinuous cell layer. With the exception of the dividing cells, details are given of all the germ cell stages. The pattern of spermatogenesis is generally typical of that observed in other Insecta but several novel observations are reported. In particular, large arc-shaped tubules associated with the nucleus and acrosome in the developing spermatid are reported for the first time and an unusual arrangement in which the axoneme is connected by amorphous strands to the mitochondrial derivatives and plasmalemma is described. The acrosome is very distinctive; the inner cone possesses a ball that fits into a corresponding socket in the nucleus. Details are given of centriole duplication in the primary spermatocyte and the stages leading to the formation of the definitive sperm plasmalemma. Where possible comparisons are made with other Coleoptera.

The sperm axoneme of Hypselodoris tricolor forms from a single centriole that is located initially beneath the plasma membrane and then migrates to the nuclear surface. A conspicuous centriolar adjunct-like formation is present in the neck of midspermatids, but it becomes very reduced at the end of spermiogenesis. In spermatocyte and spermatid mitochondria, intracristal bodies originate from the accumulation of a dense material in some cristae. From our observations and foregoing reports, it may be concluded that the process of sperm tail differentiation in opisthobranchs resembles that in pulmonates, whereas it differs in many respects from that occurring in prosobranchs. The appearance of intracristal bodies in modified mitochondria seems to be a special feature of spermatogenesis in the opisthobranchs that does not occur in the two other groups of gastropod molluscs.

Spermatozoa of the basommatophoran pulmonate families Ellobiidae (Ophicardelus ornatus Ferussac), Amphibolidae (Salinator fragilis Lamarck, Salinator solida von Martens), Siphonariidae (Siphonaria funiculata Reeve) and Lymnaeidae (Lymnaea lessoni (Deshayes)) were studied using transmission electron microscopy. Spermatozoa of all species, like most euthyneuran spermatozoa, possess (I) an acrosome composed of an apical vesicle and acrosomal pedestal (many differences between families), (2) a helically keeled, posteriorly invaginated nucleus, (3) a midpiece composed of paracrystalline and matrix materials and a variable number of incorporated glycogen-filled helices (one in Salinator and Siphonaria, two or three in Lymnaea, three in Ophicardelus) and (4) an axoneme associated with coarse fibres (periodically banded in "neck" region) and rows of intra-axonemal granules. The wide diversity of spermatozoon structure in the species studied, in particular the midpiece structure of Siphonaria (which resembles closely that of certain opisthobranchs) indicates that the Basommatophora may not represent a valid taxonomic unit. A comparison of basommatophoran sperm with other euthyneurans and with euspermatozoa of prosobranchs is given.

Ultrastructural observations on spermiogenesis and spermatozoa of selected pyramidellid gastropods (species ofTurbonilla, Pyrgulina, Cingulina andHinemoa) are presented. During spermatid developement, the condensing nucleus becomes initially anterio-posteriorly compressed or sometimes cup-shaped. Concurrently, the acrosomal complex attaches to an electrondense layer at the presumptive anterior pole of the nucleus, while at the opposite (posterior) pole of the nucleus a shallow invagination is formed to accommodate the centriolar derivative. Midpiece formation begins soon after these events have taken place, and involves the following processes: (1) the wrapping of individual mitochondria around the axoneme/coarse fibre complex; (2) later internal metamorphosis resulting in replacement of cristae by paracrystalline layers which envelope the matrix material; and (3) formation of a glycogen-filled helix within the mitochondrial derivative (via a secondary wrapping of mitochondria). Advanced stages of nuclear condensation (elongation, transformation of fibres into lamellae, subsequent compaction) and midpiece formation proceed within a microtubular sheath (‘manchette’). Pyramidellid spermatozoa consist of an acrosomal complex (round to ovoid apical vesicle; column-shaped acrosomal pedestal), helically-keeled nucleus (short, 7–10 μm long, shallow basal invagination for axoneme/coarse fibre attachment), elongate helical midpiece (composed of axoneme, coarse fibres, paracrystalline and matrix materials, glycogen-filled helix), glycogen piece (length variable, preceeded by a dense ring structure at junction with midpiece). The features of developing and mature spermatozoa observed in the Pyramidellidae are as observed in opisthobranch and pulmonate gastropods indicating that the Pyramidelloidea should be placed within the Euthyneura/Heterobranchia, most appropriately as a member group of the Opisthobranchia.

The spermatozoon of Tornatina sp. has been studied with phase-contrast light microscopy and transmission electron microscopy. The head of the spermatozoon consists of an elongate acrosome which caps the apex of an unusually complex, helical nucleus. This elaborate nuclear morphology has not been previously reported, but possibly is found in other opisthobranch gastropod spermatozoa. An axoneme is inserted deeply into the base of the nucleus whilst posterior from the nucleus, the axoneme is ensheathed successively by the mitochondrial derivative (midpiece) and 'glycogen' granules (glycogen piece). The midpiece exhibits fine structure similar to that observed in other euthyneuran spermatozoa (paracrystalline and matrix materials) and possesses a single helical compartment filled with what are probably glycogen granules. A dense ring structure occurs at the junction of the midpiece and glycogen piece. The spermatozoon of Tornatina and other gastropods (prosobranch and euthyneuran) are compared.

SummaryMature spermatozoa of drone honeybees (Apis mellifera), obtained from seminal vesicles, were examined with an electron microscope by negative staining and by serial sectioning. The structure is described, and illustrated in photomicrographs.

The main features of the Nematode sperm cell are the absence of a flagellum and of an acrosome. Transition forms have never been described, as in other animal phyla also reaching the aflagellate condition, like Platyhelminths and Arthropods. The absence of the flagellum must be considered as a definitive acquisition in the group. In addition, centrioles have been demonstrated to be lacking in most cases. The absence of the acrosome is the second general feature of the Nematode sperm cell. Among other features, more or less common to the Nematodes, the most important and general is the presence in the cell periphery of spheroidal membranous vesicles, originated from the Golgi complex but not involved in fertilization or in the production of ascaridin granules. These are absent only in the Ascarid Aspiculuris and the Dorylaimiid Xiphinema, both kinds of sperm having a peculiar shape. These granules are possibly involved in cell motility. Some Nematode sperm have proteinaceous crystalline inclusions originated from the rough endoplasmic reticulum, called ascaridin granules, the role of which remains obscure. A third important feature is the absence of a nuclear envelope, characterizing all described Nematode spermatozoa, the only exception being the Enoplid Mesacanthion, which seems to be for this reason the most primitive model in the group. Other features are the reduced number, or total absence of, the chondriome, an amoeboid movement not owing to an actomyosin system and a dense halo of 10-nm filaments surrounding the perinuclear cytoplasm. In this apparently homogeneous picture, three main evolutionary steps can be recognized. The first one, represented by the primitive Enoploid Mesacanthion, is that of a sperm conserving the nuclear envelope, surrounded by a few mitochondria and many membranous vesicles. The second, the most typical of the group, present in high Enoplida, and in Rhabditida, Strongylida, Ascarida, Spimrida, Trichinellida, is that of roundish, amoeboid spermatozoa devoid of a nuclear envelope but containing mitochondria, membranous vesicles, filaments, microtubules, sometimes centrioles, and sometimes ascaridin granules. The third step is apparently a simplification of the second; in fact, in Tylenchida and Dorylaimiida, the sperm is devoid of membranous vesicles, while in Mononchida and Dioctophymatida it is devoid of mitochondria. Aspiculuris, also devoid of membranous vesicles and having a big mitochondrial derivative, can be assigned to the same level. Nematode sperm evolution does not seem therefore to be a progressive acquisition of new characters, but rather a radiation from an already perfect model of some further simplifications occurring in parallel in most of the orders.

Spermatogenesis in the honey bee (Apis mellifera L.) differs from the process in diploid insects in several ways. The primary spermatocytes in the haploid drone undergo an abortive first meiotic division and, further, an unequal division of the secondary spermatocyte occurs. The result is two spermatids rather than the typical four. Associated with the first meiotic division, a centriole replication process occurs resulting in supernumary centrioles; the latter are eliminated from the cells through cytoplasmic blebs prior to the second meiotic division. During the centriole replication process, several single annulate lamellae appear to be differentiated from pre-existing lamellae of endoplasmic reticulum. An amorphous granular material is observed to surround the replicating centrioles, and it is similar to material located in the pores of the annulate lamellae and nuclear envelope. Because of the specific orientation which the annulate lamellae illustrate relative to the replicating centrioles, it is postulated that they are somehow involved in the accumulation of material utilized in centriole replication. The secondary spermatocyte spindle has associated with it a nuclear “wall” composed of alternate vesicular and compact layers of endoplasmic reticulum. The innermost layer of this wall appears to give rise to the spermatid nuclear envelope. Spermatocytes are interconnected by intercellular bridges throughout the process of spermatogenesis and it is postulated that this syncytium synchronizes the division process. Spermiogenesis in the honey bee is similar to that observed in a number of other insects.

In this paper the spermatozoon of a plecopteran and of a trichopteran is described. The former is an “orthopteroid type” spermatozoon, with the following peculiarities: acrosome lying in lateral position with respect to the nucleus; proteinaceous rodlet arising from the adjunct centriole and flanking the two mitochondrial derivatives in the tail; accessory fibers of the axial-filament complex hollow even at maturation. This spermatozoon is therefore quite different from Odonata and Ephemeroptera sperms previously described, and it represents the simplest case of structure of the outer accessory fibers known in insects. The spermatozoon of the trichopteran exhibits the following characteristics: absence of an acrosome, a third supernumerary proteinaceous slender fibril between the two principal central ones, only one mitochondrial derivative entirely occupied by parallel transverse cristae and lacking a crystalline axis. The outer accessory fibers of the flagellum are 300 A in diameter and, in this respect, closely recall those of Lepidoptera, comparatively reexamined in this paper. Like the principal central units, these fibers are filled with glycogen-like polysaccharides and proteins, and they are longer than the 9 principal peripheral doublets. This model of Trichoptera and Lepidoptera outer fibers is quite different from the pattern hitherto described in other insects.

The mature spermatozoon of Spadella cephaloptera belongs to the filiform type. At the front end it contains a membraneous cap, which may be an acrosomal structure, and some beaded sacs. A crystal structure is found in these sacs in spermatid stages. Near this front end there is a centriolar structure. A very elongated mitochondrial derivative runs through most of the sperm. In the central half of the sperm there is a structure composed of some longitudinal sacs lying alongside the axonema. The nucleus is situated in the hind end, just in front of a free flagellum. The spermatozoon is highly unique, but to some extent it agrees with spermatozoa found among arthropodes and gastropodes.

Resume Les transformations du chondriome pendant la spermatogenese ont ete etudiees a l'aide du microscope electronique chez une cinquantaine d'especes animales zoologiquement tres variees. Elles sont decrites en detail pour trois d'entre elles: Rat, Testacella (Mollusca, Gastropoda), Pieris (Insecta, Lepidoptera). Chez ces especes le chondriome, d'ultrastructure habituelle au depart (spermatogonies), se multiplie abondamment et subit des modifications qui leguent au spermatozoide des corps mitochondriaux d'ultrastructure inhabituelle. Les faits les plus saillants de cette evolution sont: I. Chez le Rat: (1) l'apparition d'une substance nouvelle, claire, nommee pseudomatrice, dilatant les espaces intermembranaires des cretes (espaces intracristaux); (2) l'augmentation d'opacite des espaces matriciels, avec une reduction concomitante de leur volume qui amene une inversion des contrastes par rapport a l'ultrastructure normale; (3) l'expulsion de la pseudomatrice; (4) l'allongement et l'enroulement autour du flagelle de ces mitochondries modifiees, qui finalement s'alignent les unes derriere les autres, tout en conservant leur individualite, en deux helices, jointives et de pas constant, entre lesquelles s'intercalent localement une troisieme, et parfois une quatrieme helices; II. Chez la Testacelle: (1) l'apparition d'une pseudomatrice, accompagnee d'une reduction et d'une opacification des espaces matriciels, comme chez le Rat; (2) la disposition en spheres emboitees des lames matricielles; (3) le groupement periflagellaire de ces mitochondries a structure concentrique; (4) leur fusion en un seul chondriosome, de dimensions gigantesques; (5) l'evanouissement des structures de l'internum mitochondrial, veritable metamorphose au cours de laquelle membranes, matrice, pseudomatrice et granules disparaissent, tandis qu'apparaissent des domaines ordonnes; (6) la croissance des domaines ordonnes, qui s'organisent finalement en deux manchons concentriques dont la structure, paracristalline, a ete analysee, et dont la nature, non etablie avec certitude, est supposee proteique; il est suggere que les elements constitutifs du reseau paracristallin, petits bâtonnets creux de 90 A. representent un etat particulier des proteines respiratoires; (7) la demixtion de substances, supposees lipidiques en majorite, d'ultrastructure variee, qui forment trois helices distinctes (dont deux sont jumelles) logees entre les deux manchons paracristallins; cites sont errones, douteux ou insuffisamment prouves. (4) Cette augmentation du chondriome est favorable a la recherche des modalites de la multiplication mitochondriale; les constatations faites sur le Rat conduisent a emettre l'hypothese que de nouvelles mitochondries se forment par induction au voisinage immediat d'une mitochondrie preexistante, ou par croissance et scission d'une mitochondrie-mere; elles forment alors des groupements particuliers de mitochondries qui terminent leur maturation, puis se dispersent dans le cytoplasme. Dans les deux cas, la presence d'une mitochondrie initiale serait necessaire. III. Cytochimie et biochimie. Les colorations classiques apres fixation, la coloration supravitale au vert Janus B et la detection de l'activite succino-deshydrogenasique a l'aide du tetrazolium nitro-bleu, mises en parallele avec les images de la microscopie electronique, concordent a montrer que, a la fin de la spermatogenese, les enzymes respiratoires membranaires sont non seulement presentes, mais concentrees, meme dans les cas ou la morphologie est profondement aberrante. Les implications physiologiques de cette concentration enzymatique sont discutees.