42O E. L. SHAFFER. 



distinguishable from the head of the spermatozoon, and hence 

 there is no well-defined middle-piece. 



In the youngest spermatid there is always present a cyto- 

 plasmic body of a refringent nature which takes the plasma 

 stain (Figs. 19, 38). One portion of it is more compact, while 

 the other part is in the form of a vacuole containing a deeply 

 staining (haematoxylin) body. This structure is undoubtedly 

 a spindle derivative, but whether it represents the sphere material 

 or the mitosome I am unable to state. As to the origin of the 

 deeply staining body contained within it, I am equally unable 

 to explain. It may possibly represent a portion of the cell- 

 plate which has become detached from the cell wall and has 

 become encompassed in the remains of the spindle. 1 In older 

 spermatids a compact portion of the spindle derivative is found 

 lying near the nucleus in that part of the spermatid which is 

 destined to give rise to the head end of the spermatozoon (Fig. 

 21). In later stages, as the nucleus becomes laterally com- 

 pressed, this structure is transformed into the acrosome. The 

 remainder of the spindle derivative is sloughed off into the tail 

 of the spermatozoon and gradually disappears. 



4. Discussion. As has been previously stated, the axial fila- 

 ment in Passahis arises in connection with the centrosome. 

 Munson (1906) has expressed an entirely different view con- 

 cerning its origin in Papilio. His view is that the axial filament 

 represents a much compressed portion of the cytoreticulum and 

 has no relation to the centrosome. Accordingly, he finds that 

 in the stages of development of the axial filament occasionally 

 three or four filaments may be present in a single spermatid, 

 but these finally unite into a single thread. Paulmier (1899) 

 has described double and quadruple spermatids in which two 

 or four axial filaments were present, but each was connected to a 

 centrosome. Munson's view arises from the fact that he has 

 assigned a wholly different function to the centrosome. His 

 figures of the spermatids of Papilio show spindle derivatives 

 each containing a deeply staining body which he interprets as 



1 Duesberg (1908) figures a similar spindle derivative in the spermatid of the 

 rat which he designates as the "idiozome." It also consists of a vacuolar portion 

 which contains a deeply-staining granule which is not a centrosome, just as in 

 Passalus. 



