328 ENTOZOA. 



uterine horns. During the passage of the germs down the vitelh- 

 gene portion, the yelk granules have surrounded the nucleated 

 germ-vesicles so as to be capable of separation into distinct 

 granular masses ; and, still lower down, they assume, first, a poly- 

 hedral or flattened sub-triangular figure, and then, subsequently, a 

 more or less clavate outline, the narrow ends, or pedicles, of which 

 converge, as it were, towards a central granular longitudinal 

 axis, termed the rachis. At a later stage within the upper part 

 of the oviducal portion of the reproductive tube, the unimpreg- 

 nated ova separate fi^-om the central granular rachis, and shortly 





Fig. 71. — Kuptured egg of Ascaris mystax, displaying the sculptured chorion, delicate vitelline 

 membrane, and grantdar yelk ; highly magnified. — Claparede. 



afterwards they are, in this situation, brought in contact with the 

 thimble-shaped spermatozoa of the male. According to Nelson the 

 male elements enter the ovum at any point, because, in his opinion, 

 in which Thomson also shares, the granular mass, though well 

 defined, is not, at this period, surrounded by a true yelk-membrane ; 

 but Meissner, on the other hand, affirms that the ova are 

 enveloped by a delicate membrane, and that the spermatozoa enter 

 at the point where the pedicle separated from the central rachis. 

 This opening he terms the micropyle. At all events, the union of 

 these different sexual elements constitutes the very act of impreg- 

 n^-tion. Similar phenomena have been witnessed by myself in 



