78 ENTOZOA. 



As in other nematodes at a certain stage previous to impregna- 

 tion, tte ova are triangular or irregularly polygonal in outline, and 

 the thin limiting membrane by which they are surrounded encloses 

 finely granular contents (Plate V., Fig. 7) . In the perfectly developed 

 egg, the external chitinous chorion presents the same characters as 

 in Trichocephalus dispar. At either pole of the egg, where the shell 

 terminates abruptly, an inner transparent membrane projects in the 

 form of a papilla (Fig. 8). When fully developed, the ova have 

 a longitudinal diameter of afo to the Jo of an inch. In none of 

 the eggs which I have examined were there any traces of an embryo, 

 but I have commonly found them in the earliest stages of yolk-seg- 

 mentation. Some little while ago Kuchenmeister expressed his 

 opinion that Trichocephalus had some genetic relation with Trichina, 

 but the series of able researches by Virchow and R. Leuckart, 

 carried on independently, have shown this opinion to be erroneous. 

 More recently, Davaine strove to determine the development 

 and migrations of Trichocephalus by direct experiment, and accord- 

 ingly he found that the embryonic formation only took place within 

 the egg after the ova had been immersed in water for a period of 

 six months. From this, therefore, it may be surmised that the 

 escaped embryos ultimately gain access to our bodies in a passive 

 manner when swallowed with the waters we drink. At all events 

 it satisfactorily explains why my own feeding experiments with the 

 fii-esh eggs of Trichocephalus affinis from a Giraffe, merely led to a 

 negative result. 



Genera. — Monopetalonema, Diesing ; Oongylonema, Diesing ; 

 Bicheilonema, Diesing ; Tricheilonema, Diesing ; Tetracheilonema, 

 Diesing; Filaria, MiiUer; = (in part) Fusaria, Zeder; = The- 

 lazia, Bosc ; BracvMcuhis, Kaempfer ; Icthyonema, Diesing ; Dipe- 

 talonema, Diesing ; Solenonema, Diesing ; Filaroides, Van Beneden ; 

 Trichosoma, Dujardin ; = Eamularia, Rudolphi ; = (in part) 

 Capillaria, Zeder; Trichocephalus, Dujardin; = Trichuris, Eoe- 

 derer ; Onchophora, Diesing ; Thominx, Dujardin ; Eucoleus, Dujar- 

 din ; Oalodium, Dujardin ; Liniscus, Dujardin ; Sclerotrichum, 



