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Ovarian morphology was studied from the inception of meiosis in the cat, mink and ferret. It was shown that "open connections", allowing cellular contact, existed between the intra-ovarian rete cords and the groups of germ cells as well as between the surface epithelium and the germ cells. The germ cells in the innermost part of the cortex and lying in contact with the rete cells were those which were the first to enter meiotic prophase. Later, the more peripheral oogonia transformed to oocytes. The first follicular formations occurred at the innermost part of the cortex. The granulosa cell layers were in open connection with the intra-ovarian rete cords. In the mink and ferret, a certain part of the rete system at the hilus differentiated into the hilar rete body. In all animals, the extra-ovarian rete cells were actively secreting. It is proposed that the rete system interacts with the cortex, initiating the start of meiosis and that the rete cells as well as cells of the surface epithelium contribute to the granulosa cell layer.

Ultrastructural observations of the ovary and uterus of Dirofilaria immitis reveal some characteristics of oogonia, oocytes, and uterine sperm. Oogonia are confined to the distal portion of the ovary including a blind tip, where a morphologically distinct terminal cap cell was not observed. These cells contain a nucleus with a nucleolus, numerous dense bodies, scanty ribosomes, lipid droplets, and an occasional mitochondrion. Endoplasmic reticulum is lacking and Golgi complexes were observed only in fully grown oogonia. Primary oocytes located in the middle portion of the ovary are large, elongate, and have a complete set of organelles including many small mitochondria, fragmentary endoplasmic reticulum, ribosomes, Golgi complexes, and very few dense bodies. These cells are arranged into many rosettes about central cytoplasmic masses, the rachises, to which they maintain cytoplasmic continuity by pseudopodlike processes. The rachises contain no organelle except a few dense granules and are bound by winding membranes. Oocytes from the proximal portion differ from those of the middle portion of the ovary in their larger size, round shape, absence of many organelles, presence of small dense granules, and lacking a rachis. Dense bodies are specific to the oogonia and exhibit DNase susceptibility and a positive reaction for a mitochondrial enzyme. These findings together with their decreased number and a concomitant increase of mitochondria in the oocytes suggest a relationship between these bodies and mitochondria. Uterine sperm of D. immitis are of the amoeboid type and contain several chromatin masses without a nuclear envelope, many mitochondria, and specialized membranous organelles referred to as mesosomelike vesicles. The vesicles are probably originated from the sperm plasma membrane. Upon fertilization, the entire spermatozoon penetrates the oocyte and its contents are gradually dissolved in the ooplasm with a simultaneous appearance of large numbers of ribosomes at the site of dissolution. Ribosomes were later found in the nucleus. A pronucleus was not observed. These findings are basically in agreement with those described for Ascaris but differ in the morphologic features and number of rachises, presence of dense bodies, absence of refringent granules in the oocytes and the absence of a refringent body and presence of several chromatin masses in the sperm.

This paper reports on the structure of rat primary oocytes, as observed with the electron microscope. Four main components are described in the cytoplasm: Golgi apparatus, centrioles, mitochondria and multivesicular bodies.

Developing rat ova have been studied with the electron microscope. Special attention was paid to relations of ova to the granulosa cells, the developmental stages of ovarian follicles, and the cytology of the unfertilized tubal ova. The relationship of the oocyte to the surrounding granulosa cells was found to change from one of a simple apposition of the plasma membranes to a complex interdigitation of microvilli from the ovular surface and processes from the granulosa cells extending into the matrix of the zona pellucida. This complex interrelation is maintained until the formation of the first polar body is initiated. At this time no microvilli are found and the oolemma presents a gently undulating outline. Also at this time, a perivitelline space forms and the granulosa cell processes retract. In the unfertilized tubal ova no microvilli are present and the processes of the follicular cells are completely withdrawn. The cytoplasmic elements of the oocyte in various stages of development are described in some detail. Of particular interest is the change noted in position and degree of aggregation of the Golgi complex as maturation proceeds. The distribution and structural characteristics of the mitochondria, ergastoplasm, dense particles, and multivesicular bodies are described.

SummaryPregnant rats were exposed to doses of 25 to 2 × 100 r of x-rays at varying times between the 13th and the 20th days after insemination. Female offspring were killed at 25 days post partum, and the number of oocytes was estimated from serial sections of the ovaries.The population of oocytes in the irradiated ovaries was found to depend both on the dose of x-rays administered and on foetal age at the time of exposure.The period of maximum radiosensitivity, which occurred on the 15th day of gestation, was found to coincide with a high rate of mitotic division of oogonia.

Dose-rate dependence of radiation-induced mutation rate was studied in silk-work spermatogonia and oogonia by the use of the specific locus method. Both sexes of a wild-type strain were exposed to x rays, Cs/sup 137/ gamma -rays of high dose rate, or to Co/sup 60/ gamma -rays of low dose rate at a definite stage or during a definite period in early larval stages. The dose-rate ratios between the acute and chronic irradiations were 2500: 1 to 7600: 1. The total doses given were 950 r or 1000 r. Two types of dose-rate dependence of radiationinduced mutation rate were found. In one type mutagenic effectiveness of chronic irradiation is lower than that of acute irradiation (Type I) and in the other mutagenic effectiveness is higher in chronic irradiation than acute irradiation (Type II) The former is observed only in the very prevalent in the testis, while the latter is found when later stages of spermatogonia or oogonia are irradiated. For Type I dose-rate dependence, repair of primary mutations seems to the responsible, whereas for Type II dose-rate dependence selective killing of a specific type of cells by intense exposure seems to play an important role. The relationship between our finding andmore » that of Russell is discussed. Radiation-induced mutation frequency is remarkably high at the very early stage of larva, i.e., around the time of hatching when the primordial germ cells are prevalent in the gonads. (auth)« less

A certain degree of synchronization of germ cell differentiation is a general feature of mammalian oogenesis. In the rat (3, 10), mouse (4), and rabbit (15, 16), germ cell differentiation is highly synchronized in that there is a direct correspondence between fetal age and predominant stage of cellular activity. In the guinea pig (11), monkey (2), and man (1), the synchronized pattern is less apparent because of a considerable overlapping of mitosis, meiosis, and degeneration. Correpondence between age and stage of differentiation of a significant percentage of germ cells is found even in these species, however. In the course of an electron microscopic study of ovarian development in the newborn rabbit, we have observed that the synchronization of the oogenetic process finds expression not only in the close relationship between fetal age and stage of cellular differentiation, but also in the maturation of the germ cells in groups and in the synchronous differentiation of all the cells in each group. Such synchronization appears to be related

The ovary of sexually mature non-pregnant guinea pigs has been studied by light and electron microscopy. The electron micrographs of oogonia reveal a large nucelus with an irregular nucleolus composed of dense granules arranged in reticular fashion. In the cytoplasm are many mitochondria and a few elements of the endoplasmic reticulum. The large “yolk nucleus” is osmiophilic after preparing material by Kolatchew's technique. Submicroscopically, this body is composed of many double membrane lamellae and vesicles of varying sizes. It is referred to as Golgi material. The plasma membrane of oogonia is smooth and in direct contact with that of the flattened follicular epithelial cells. The cytoplasm of primary oocytes contains many vesicles, regions displaying small masses of Golgi complexes, multivesicular bodies, mitochondria and a scant amount of cisternae of the endoplasmic reticulum. The plasma membrane is thrown into protoplasmic projections in the form of microvilli. The cytoplasm of cells forming the corona radiata consists of the same cytoplasmic constituents as the oogonium and primary oocyte. The endoplasmic reticulum, however, is more highly organized. These cells appear stellate and their processes end on the plasma membrane of the oocyte in the form of desmosome-like areas. The zona pellucida appears to be composed of a homogeneous, apparently structureless, material of relatively low density. Within this material are embedded the microvilli of the primary oocyte and the processes of the follicle cells. A suggestion is made concerning a possible mode by which the primary oocyte receives its nutrient materials.

In S. richardsonii, unlike its testis, the whole of the ovary is fertile. The oogonia pass through seven maturation stages to form the ripe ova. The residual oogonia are responsible for the development of the new crop of oogonia. The zonation of the ooplasm reveals that a majority of the oocytes have a darkly stained inner and a lightly stained outer zone. The yolk nucleus probably has some relationship with the process of vitellogenesis. The nucleoli are produced by the division and fragmentation of the nucleolus. Extrusion of nucleoli appears to be associated with the formation of yolk. The formation of yolk globules in the oocyte begins in the periphery of the ooplasm and moves inward till the whole of the ooplasm in impregnated with yolk. As the yolk vesicles are PAS-positive in this fish, they contain mucopolysaccharides. The ovarian cycle can be divided into five stages. The ovary becomes much enlarged and distended in the month of October and delicate and thin in March. The spawning season extends from late October to December and the ovary exhibits asynchronism.

The nucleoli of oogonia and oocytes of rat ovaries during fetal and neonatal life were studied by light and electron microscopy. An evolution from atypical to typical nucleoli was shown. Nucleoli undergo a gradual increase in size and change from dense fibrillar bodies to complete nucleoli with pars fibrosa, pars granulosa, pars amorpha, and associated chromatin.

Quiescent oocytes of the monkey Cebus albifrons were examined with the electron microscope. In many respects the ultrastructure of these cells was similar to that of other mammalian species. Elongate and oval mitochondria, lamellar Golgi complexes, small profiles of smooth endoplasmic reticulum, and vacuolar organelles were randomly distributed around a round nucleus which usually contained a nucleolus and clumps of heterochromatin. Among the unusual morphological characteristics of these oocytes are 'membranous aggregates', membrane-bound organelles containing a complex of convoluted membranes, some very dense rod-like structures and a droplet of moderate density which resembles lipid. A similar droplet is frequently found in mitochondria. Rough endoplasmic reticulum is abundant in many of these oocytes, forming parallel arrays and concentric rings around the nucleus. Folded membrane complexes, apparent elaborations of smooth endoplasmic reticulum, are frequently found in the cytoplasm in continuity with cisternae of smooth and rough endoplasmic reticulum and associated with vesicles which often contain flocculent material. The morphology of Cebus oocytes suggests a greater rate of steroid and protein synthesis, transport, and storage than is usually indicated by the ultrastructure of other mammalian oocytes.

Foetal rats were exposed to 100 r (acute X-irradiation) at 15.5, 16.5 and 17.5 days of intrauterine life, and killed at daily intervals up to 20.5 daysp.c. The populations of normal and degenerating germ cells in irradiated ovaries were estimated by the volumetric method of Beaumont & Mandl (1962). The chromosomal configurations of germ cells were examined in both histological and squash preparations. Irradiation appears to disturb the close developmental synchronization of germ cells. Many irradiated cells also show transient changes in chromosomal morphology, and an increase in cell and nuclear volumes. The treatment induces both immediate cell death (i.e. within 24 h of exposure) and delayed cell death. The latter becomes manifest by an increase in the incidence of degenerating cells of the same type as arise spontaneously during normal development (‘atretic divisions’; ‘Z’ cells). The most severe depletion in the total population of germ cells occurs following exposure at 15.5 days, only some 13 000 germ cells being present 24 h later (cf. 37 000 in coeval controls). Their number is further reduced to about 5000 at 20.5 days (cf. 56 000 in controls). In contrast, the mean populations at 20.5 days following irradiation at 16.5 and 17.5 days areca. 16 000 and 42 500 respectively. Most degenerating germ cells are eliminated from the ovary by 20.5 days. The subsequent loss of oocytes with age (up to 25 and 100 daysp.p.) occurs at alowerrate in irradiated than in normal animals.