INSECT SPERMATOGENESIS 619 



or is possibly of centriolar origin, I have not been able to 

 determine. At any rate this seems to be a common point of 

 attachment for both acrosome and tail filament. There are 

 indications that subsequently (tig. 40 and later) the centriolar 

 ajjparatus, or a portion of it, l)ecomes shifted to the base of 

 the sperm head, but I have not found my material satisfactory 

 for a detailed study of these phenomena. 



In Callosamia the general progress of events is exactly 

 parallel to that in P y g a e r a , with the possible exception 

 of the method of orientation of the acrosome. The structure of 

 the acrosome in this moth does not permit detailed study of 

 a possible forward migration, and it is possible that the migra- 

 tion may occur in a different way. In the early figures, it will 

 be seen that the acrosome is deposited at a point some distance 

 removed from the insertion of the tail filament. As the acrosome 

 begins to elongate, however, it apparently migrates anteriorly 

 (iig. 52), and becomes attached by one end near the insertion 

 point of the axial filament (figs. 52 et seq.).^ From this point 

 on the exact course of events is uncertain, and whether or not, 

 with the elongation of the acrosome, there is a further change 

 of orientation, as in Pygaera, has not been ascertained. 

 However, appearances like that of fig. 54 suggests that perhaps 

 the acrosome at first grows posterior^, as in Pygaera, 

 and shifts later into its definitive position. As already noted 

 in Callosamia, the acrosome, as originally deposited, is 

 relatively much smaller than in Pygaera (figs. 50 and 51), 

 and we should therefore expect its later stages to be much more 

 dehcate in structure. As a matter of fact this expectation is 

 exactly realized, and almost from the beginning of elongation 

 the acrosome has a thread-like form, in which it is impossible 

 to distinguish the two acrosomal constituents (figs. 51 to 59). 



The various steps in the forward growth of the acrosome 

 are shown clearly in figs. 56 to 59, and present no points of 

 special interest. The length of the acrosome in the mature 

 sperm as compared to the length of the sperm head is much less 



^ It is possible that a similar migration occurs in Pygaera, where 

 it would be masked by the large size of the acrosome. 



