142 ZOOLOGY 



is vesicular, and inside it there is to be found an acrosomal granule 

 (Figs. 64-66, E). In Paludina (Gatenby, 30d), the acrosome is 

 granular, and may be either the acrosomal granule or else a limiting 

 form of the vesicular type (Fig. 63, E). In the Acrididae and certain 

 moths (Bowen and Gatenby), a complex acroblast is formed. Each 

 Golgi body forms an acrosome on its own (Fig. 65, D). These 

 vesicles then fuse together to form a compound acrosome 

 (Fig. 65, D). 



The acrosome is deposited towards the surface of the nucleus, 

 and its movement to the future anterior end of the sperma- 

 tozoon may be accomplished in one of two ways. For example, in 

 the Hemiptera the vesicle is deposited on to the nuclear membrane, 

 and moves over the surface of it to the front of the sperm (Fig. 64, 

 D, E) ; while in the mammals the vesicle and the acroblast all 

 move to the anterior position, where the acrosome is deposited and 

 the Golgi remnant (as the acroblast is called after deposition of the 

 acrosome) moves back again (Fig. 66, D, E). In both cases the 

 Golgi remnant appears to be cast off as the spermatid gets rid of its 

 surplus cytoplasm. Meanwhile the centrioles have moved round 

 the nucleus, being usually diametrically opposite the acroblast and 

 acrosome (Fig. 66, D, E). Thus at the final stage of acrosomal 

 deposition they lie posterior to the nucleus (Figs. 63-66, F, G). 



The mitochondria during the formation of the acrosome have 

 massed themselves posterior to the acroblast and formed the 

 Nebenkern (Figs. 64, 66, D). They swell up and form a vacuo- 

 lated mass (Fig. 64, D). The actual constitution of this mass 

 appears to vary considerably, and even in the same form different 

 interpretations are put upon it. As far as can be seen there are two 

 portions, an outer chromophobic and an inner chromophilic 

 (Fig. 64, D). This is reported by a number of workers, e.g., 

 Bowen and Doncaster and Cannon. The chromophilic substance is 

 variously disposed. Doncaster and Cannon speak of it as vacuolar, 

 and attribute the spireme condition (Gatenby in Lepidoptera) to 

 optical sections of the cortices of the vacuoles. Bowen, however, 

 thinks that the different patterns are due to different techni(jues (7). 

 The ultimate fate of the Nebenkern is obscure. In many forms it 

 is sloughed off with the surplus proto^^lasm and Golgi remnant, but 



