RECENT RESEARCHES ON SPERMATOGENESIS. 333' 



spreads till it occupies a hemis})here of the nucleus ; then a 

 swelling is seen at the pole of the hemisphere, which form the 

 "baton terminal" (Spitzenknopf of Meckel)^ a formation quite 

 independent of the accessory corpuscle which some observers 

 have believed to have formed this structure. The hemisphere 

 continues to thicken till it forms a hood (capuchin, Kopfkappe), 

 while the caudal filament becomes united to the nucleus by a 

 granule at the opposite pole. The protoplasm of the nemato- 

 cyst forms a hyaline tube, in which can be seen the caudal fila- 

 ment. The nucleus becomes flattened, the nuclear thickening 

 with the baton terminal disappears, but its lower limit is 

 marked by a circular line, and the mature spermatozoon is 

 formed. 



The formation of the spermatozoon, as here briefly described, 

 has many points of similarity with that above mentioned in 

 Selachians. In both there is a body formed (corpuscle pre- 

 curseur. Selachians, accessory corpuscle. Mammals), which takes 

 no share in the process. In both a caudal filament is protruded 

 in both a thickening of the nucleus forms the head, and in both 

 there is a consolidation of the plasma, which may be regarded 

 as forming the middle piece ; and here let me make a few 

 remarks on this portion of the spermatogenetic process. 



It is now well determined that the nucleus forms the head 

 of the spermatozoon, and the plasma of the spermatoblast gives 

 rise to the tail, but does the whole of each take part in the 

 process ? It seemed to me in the cases which I selected for 

 study that the head was formed by simple elongation or 

 change of shape of the nucleus, while drawing out of the 

 plasma gave origin to the tail; but it is more than probable 

 that in many cases the process is more complicated than this 

 and possible that it differs in different animals. The similarity 

 of the process in Selachians and Mammals would seem to 

 suggest that it is conducted on one plan, which plan would 

 seem to be that a portion of the nucleus — possibly the mem- 

 brane and t)ie chromatin — form the head, while a caudal fila- 

 ment forms the extreme portion of the tail, the intermediate 

 part having origin in solidification or modification of the sub- 



