146 



THE TESTES, BY V. LA VALETTE ST. GEORGE. 



drical, oval, or pyriform bodies occur with delicate capilliform 

 tails Cyclas, Unio, Anodonta, etc. (Wagner, v. Siebold). 



The seminal corpuscles of the CEPHALOPHORA present great 

 diversity of form. Gegenbaur describes those of the PTEROPODA 

 as thickened at one end, and there slightly twisted, whilst the 

 other end is continued into a fine thread which, just before its 

 termination, dilates into a small vesicle. 



Fig. 177. 



Fig. 177. Spermatozoon of Helix nemoralis. 



In the GASTEROPODA the seminal elements present very vari- 

 ous forms ; in some the head is oval, pyriform, or sometimes 

 constricted in the middle Chiton, Trochus, Patella, Haliotis 

 (Kolliker, Wagner, Erdl) ; in others the zooid is capilliform 

 and pointed at both extremities Turbo, Buccinum, Purpura. 

 In Doris the fibre increases in thickness towards the extremity, 



Fig. 178. 



Fig. 178. The two forms of spermatozoa in Paludina vivipara. 



and appears slightly twisted ; occasionally there is a poinl 

 head at one extremity Lymnceus, Planorbis, Helix (v. Sit 

 bold, v. la Valette St. George). 



The occurrence of two forms of spermatozoa, as described b 

 v. Siebold, and subsequently by Leydig in Paludina 



