48 • ENTOZOA. 



shell came under my observation, there was only this solitary 

 example to be seen, and I only observed its escape on one occasion. 

 The two seminal vesicles, standing out most conspicuously in 

 G. tenuis, are filled by a convolution of filaments, and intercom- 

 municate by a canal. The connexion of the posterior seminal 

 vesicle with the presumed testes was not perceptible ; but the 

 anterior is in continuity with the external, horny, male repro- 

 ductive apparatus. The last-named organ is characterized by 

 much variety of form, so that one may exclaim, ' Bx pene speciem.' 

 Speaking generally, we observe a peculiar, more or less curved 

 penis, grooved for the passage of semen, and an accessory sohd 

 portion which is often hooked. The latter serves, probably, as a 

 fang or organ for adhering to the vagina. In one instance where 

 the accessory portion was absent, I found two hooklets at the 

 entrance of the vagina. These, in all probability (functionally), 

 represented the same, (being formed) for the purpose of laying 

 hold of the penis when the latter was lodged within the sheath. 

 Thus Gyrodactylus becomes sexually developed, and cannot be 

 regarded merely as a kind of 'nurse.' " 



Development. — The genetic relations subsisting amongst the 

 Gyrodactyles are in some respects peculiar, and have given rise to 

 much controversy. We have abundant records of the principal 

 facts and phenomena observed in the reproductive process, and, 

 for the most part, there is little contrariety of opinion in regard to 

 such data ; but, unfortunately, the method of interpreting these 

 phenomena has, according to the source whence it has proceeded, 

 produced a very variable result. Yon Siebold, observing the sin- 

 gular mode of reproduction as it takes place in Gyrodactylus elegans, 

 arrived at the conclusion that Gyrodactyles in general were only 

 nurse-forms of some higher organism, and he pointed out, with 

 undeniable accuracy, all the birth- stages of the young one as it 

 apparently pullulated within the parent and subsequently emerged 

 an almost perfect Gyrodactyle. Yon Siebold also remarked that 

 the so-called " daughter," at the time of birth, nearly equalled the 



