140 



THE GERM-CELLS 



connection with which, may be developed secondary or accessory fila- 

 ments and other structures. At the tip the axial filament may lose 

 its envelope and thus give rise to the so-called "end-piece" (Retzius). 

 In Triton, for example (Fig. 66, F\ the envelope of the axial fila- 

 ment ("principal filament ") gives attachment to a remarkable fin-hke 



membrane, having a frilled or 

 undulating free margin along 

 which is developed a "mar- 

 ginal filament." Toward the 

 tip of the tail the fin, and 

 finally the entire envelope, 

 disappears, leaving only the 

 axial filament to form the end- 

 piece. After maceration the 

 envelope shows a conspicuous 

 cross-striation, which perhaps 

 indicates a spiral structure 

 such as occurs in the mam- 

 mals. The marginal filament, 

 on the other hand, breaks 

 up into numerous parallel 

 filDrilte, while the a.xial fila- 

 ment remains unaltered (Bal- 

 lowitz). 



A fin-membrane has also 

 been observed in some insects 

 and fishes, and has been as- 

 serted to occur in mammals 

 (man included). Later ob- 

 servers have, however, failed 

 to find the fin in mammals, 

 and their observations indi- 

 cate that the axial filament is 

 merely surrounded by an 

 envelope which sometimes 

 shows traces of the same 

 spiral arrangement as that 

 which is so conspicuous in 

 the connecting-piece. In the 

 skate the tail has two fila- 

 ments, both composed of 

 parallel fibrillae, connected by 

 a membrane and spirally 

 twisted about each other; a 



Fig. 68. — Spermatozoa of mammals, [.-/-i^from 

 BALLOvvrrz.] 



A. Badger (living). B. The same after staining. 

 C. Bat (Vesperugo). D. The same, flagellum and 

 middle-piece or connecting-piece, showing end-knobs. 

 E. Head of the spermatozoon of the bat (Rhino- 

 lophus) showing details. F. Head of spermatozoon 

 of the pig. G. Opossum (after staining). H. Double 

 spermatozoa from the vas deferens of the opossum. 

 /. Rat. 



h.c. head-cap (acrosome) ; k. end-knob; m. mid- 

 dle-piece ; n. nucleus (in B, E, F, consisting of two 

 different parts). 



