I04 



THE GERM-CELLS 



sory filaments 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 

 k '\ - ^ example (Fig. 48, F\ the 

 envelope of the axial fila- 

 ment (" principal filament ") 

 gives attachment to a re- 

 markable fin-like membrane, 

 having a frilled or undulat- 

 ing free margin along which 

 is developed a " marginal 

 filament." Towards the tip 

 of the tail, the fin, and 

 finally the entire envelope, 

 disappears, leaving only the 

 axial filament to form the 

 end-piece. After macera- 

 tion the envelope shows a 

 conspicuous cross-striation, 

 which perhaps indicates a 

 spiral structure such as oc- 

 curs in the mammals. The 

 marginal filament, on the 

 other hand, breaks up into 

 numerous parallel fibrillae, 

 while the axial filament re- 

 mains unaltered (Ballowitz). 

 A fin-membrane has also 

 been observed in some in- 

 sects and fishes, and has 

 been asserted to occur in 

 mammals (man included). 

 Later observers have, how- 

 ever, failed to find the fin in 

 mammals, and their obser- 

 vations indicate that the 

 axial filament is merely sur- 

 rounded 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 filaments, both composed of parallel fibrillce, connected by 

 a membrane and spirally twisted about each other ; a somewhat 



I^'ig- 50. — Spermatozoa of mammals. {A-F from 



B.'VLLOWIIZ.) 



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

 C. Bat {Ve^per^lgo). D. The same, fiagellum and 

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

 E. Head of the spermatozoon of the bat ( Khiiwlophus) 

 showing details. F. Head of spermatozoon of the pig. 

 G. Opossum (after staining). H. Double spermatozoa 

 from the vas deferens of the opossum. /. Rat. 



he. head-cap (apex) ; /4. end-knob (? centj'osome) ; 

 m. middle-iiiece ; n. nucleus (in B, E, i-' consisting 

 of two different parts) . 



