1910.] NATURAL SCIENCES OF PHILADELPHIA. 315 



bm soon moves toward the head, where it takes its final position and 

 appears to be transformed into the acrosome. 



Spermatids and Spermatozoa. 



The metamorphosis of the spermatid of each species here studied 

 has in most of its parts been considered in the preceding text; thus, 

 as has been pointed out, the sperm head is made up of the modified 

 nucleus of the second spermatocyte plus the head shield, while what 

 in many animals would correspond to the middle piece is in Lepi- 

 doptera only the region occupied by the two centrosomes. The 

 nebenkern which seems to be common to all insects refers, when used 

 in its original sense (Butschli, 1871), to that body in the spermatid 

 which i-> formed at least in part by the spindle fibres of the second 

 maturation division and which later gives rise to the inner tail mem- 

 brane. Many workers on insects, among whom may be mentioned 

 La Valette St. George, Platner, Erlanger, Henking, Wilcox (1896), 

 and Paulmier, trace its origin at least in part to the remnants of the 

 spindle, though Paulmier attributed only a small part to the spindle 

 fibres, believing that the nebenkern in Anasa is formed largely from 

 the yolk mass. Meves (1901), on the other hand, claims that this 

 body i- built up independently of the spindle fibres out of granules 

 which were present in earlier generations, and which are identical 

 with the yolk granules of Paulmier, the Cytomitosomen of La Valette 

 St. George, and the Mitochondria of Benda. No trace of yolk granules 

 were found in the Saturnids and the dark-staining accessory masses 

 figured for Acronycta were found to take no part in the formation of 

 the nebenkern; but, in both smear preparations and sections, the 

 nebenkern material for all the species studied was clearly traceable 

 to the spindle fibres of the second spermatocyte division. 



The problematical parts which remain to lie discussed are the 

 subsequent history of the chromatin granule and the origin of the 

 head piece and axial filament. Many writers describe the head piece 

 or acrosome as arising from the idiozome which migrates to the 

 anterior pole of the cell. The Schreiners (1908) have shown that the 

 head piece of Myxine is made up of two separate Anlagen, the primary 

 and secondary head vesicles, which are only joined in the beginning of 

 sperm ripening: the primary head vesicle formed from the sphere 

 takes its place after the second division, while the secondary head 

 vesicle remains in tlie opposite part of the cell near the centrosome 

 and only reaches its final position during the beginning of sperm 

 ripening. A third view is that of Lenhossek (ISO!)), who derives the 



