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.

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