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1. The lepidopteran nebenkern passes through a series of condensation phenomena which are essentially similar to those previously described in Hemiptera. 2. The structure of the chromophilic material is probably that of a plate-work rather than a spireme. 3. The central substance is developed in the nebenkern exactly as in other insects. 4. The Golgi bodies in all probability give rise each to a small vesicle, these vesicles fusing gradually to form the acrosome. 5. As in other insects, the Golgi bodies are not directly transformed in the building up of the acrosome, but, after giving rise each to its miniature acrosomal vesicle, they pass back along the tail and are probably cast out of the sperm along with other detritus in the concluding stages of spermiogenesis. 6. The essential parallelism existing between the formation of the sperm in Lepidoptera and in other insects, especially the Hemiptera, is particularly emphasized.

A helical structure which had previously been reported in the cytoplasm of many cell types in the desert locust, Schistocerca gregaria, was found in large quantities in the developing male germ cells. The helices were isolated from these cells and negatively stained. The helices, which lie free in the cytoplasm of spermatogonia, primary spermatocytes and secondary spermatocytes (sometimes associated with a second type of helix, a double helix), closely invest the outer surface of the Nebenkern membrane in spermatids. As the Nebenkern elongates, the helices gradually disappear and are replaced by microtubules. The mitochondrial derivatives of the Nebenkern, which form part of the sperm tail, are in late spermatids completely surrounded by a sheath of parallel microtubules.

The most important conclusion of this investigation is that the crab spermatozoon, in spite of its fantastic form, is with respect to its components exactly like a typical sperm. It possesses a cup-shaped nucleus with the margin of which the ring-like acrosome is fused. The mitochondria-like mass of Koltzoff, Binford, and Fasten are the fused Golgi elements destined to form the acrosome. The cavity of the cup is completely filled by the mitochondria, vesicle, corresponding to the ‘primary vesicle’ of Fasten. The mouth of the cup is very efficiently plugged by the ring-like, distal centrosome which is identical with Fasten's ‘chromatin ring’. At the bottom of the mitochondrial nebenkern lies the vesicular, proximal centrosome answering to the description of the ‘secondary vesicle’ of Fasten. Between the two centrosomes runs a thick axial filament (Fasten's central body). Evidence has been produced that at the time of fertilization the unusual form of the sperm changes into that of a typical one. In the primary spermatocytes of Paratelphusa spinigera there are no ‘chromatoid bodies’ as described by Fasten in similar cells of Cancer. On the other hand, both in the spermatocyte and the spermatogonium of Paratelphusa, there is the typical Golgi-idiosome complex.

1. The spermatid of the house-cricket, Acheta domesticus, has been studied by the use of vital dyes, histochemical tests, and electron microscopy. 2. The acroblast consists of an outer and an inner part. The former, which contains lipids and a neutral mucopolysaccharide, is seen in the electron micrographs to consist of parallel lamellae. In section these appear to be arranged in the form of a horseshoe. The internal part of the acroblast gives feeble reactions for a neutral mucopoly-saccharide and for a lipid. In electron micrographs it is seen to contain minute vesicles. 3. The acrosome arises within the acroblast. It gives a strong reaction for neutral mucopolysaccharide. It appears to be devoid of internal structure. 4. The Nebenkern, formed by the fusion of all the mitochondria in the young spermatid, exhibits the ‘cristae’ characteristic of ordinary mitochondria. The reactions of this structure with vital dyes and acid fuchsine also parallel those of the mitochondria. Histochemical tests indicate the presence of a lipid. 5. The periphery of the nucleus of the late spermatid shows a radial structure.

(1) The ovotestis of Helix aspersa is formed of fingerlike diverticula. The latter are hollow at their lower ends, which connect to the hermaphrodite duct, while the upper ends contain more yolk, and are filled completely with metamorphosing male cells. (2) According to the manner of derivation--that is, the nutrimental conditions of the locality from which new cells arise, and the number (if any) of times which these new cells divide--there are quite wide differences in the individual generations derived from and under such varying conditions. (3) These differences are found in nucleus, mitochondria, Nebenkern, and general cell volume. (4) The mitochondria vary in size and number, and such variation seems to be caused by the varying number of spermatogonial divisions in different regions of the ovotestis. (5) In the early spermatid smaller mitochondria, the micromitochondria appear in an unknown way near the region from which the axial filament takes its origin from the centro some applied to the nucleus. These micromitochondria are about one-fourth the size of the other, or macromitochondria. No perceptible variation in size of the micromitochondria of various generations has been found. (6) The micromitochondria form the front sheath of the sperm; the hind region of the micromitochondrial sheath intercommunicates with the macromitochondrial sheath, which follows behind. (7) The Nebenkern does not apparently become absorbed into the substance of the mitochondrial sheath. A sloughing off appears to take place. (8) The minute cytology of the derivation of the sperms, eggs, and nurse-cells is described. (9) The determination of the sex of the indifferent cell seems to be brought about by a variety of causes. The explanation of femaleness by presence of yolk cells is held to be inadequate, for male progerminative cells also appear in regions choked with yolk. (10) The probable function of the Nebenkern is discussed.