VI 



PHYLUM NEMATHELMINTHES 



303 



distinct. In the female Gordius (Fig. 252, C) the lateral canals of 

 the body-cavity (ut.) are modified to act as ovaries and oviducts. 

 They give off a series of regularly arranged lateral diverticula from 

 the cells lining which the ova are derived (Fig. 252, A, and Fig. 

 250, div.). Behind, each of these lateral canals becomes a narrow 

 tube or oviduct. These open into a median chamber with glandular 

 walls, the uterus (vag.), and into this there also opens the duct of a 

 spermotheca or receptaculum seminis (spth.) for the reception and 

 storage of the sperms received in copulation. The uterus is con- 

 tinued backwards by an atrial cavity opening along with the intestine 

 in a cloacal aperture (Fig. 252, gnp.) at the posterior end of the 

 body. In the male (Fig. 252, B) the lateral canals are unsegmented 



int 



v.nv.cd va & 



FIG. 252. Gordius. A, horizontal section of female, showing ovaries (ovy) attached to mesen 

 tery (mes.) ; b. w. body-wall. B, posterior extremity of male, sagittal section. 6. c. 

 coagulated mass of sperms (?) ; cl. cloaca ; int. intestine ; t. tail ; v. nv. cd. ventral nerve- 

 cord ; vs. sem. vesicula seminalis or sperm-sac. C, posterior extremity of female, sagittal 

 section, gnp. cloacal aperture ; spth. spermatheca ; ut. lateral canal ; vag. uterus, 

 followed posteriorly by atrium ; v. nv. cd. ventral nerve-cord. (After Vejdowsky.) 



tubes testes or sperm-sacs (vs. sem.) from the cells bordering a 

 portion of which sperms are developed. From each of these at its 

 posterior end a narrow vas deferens passes backwards to open into 

 the cloaca (cl). The latter, with a ventrally-placed opening, has 

 a muscular wall and is probably capable of being everted to serve 

 as a penis. In Nectonema the entire genital apparatus is simpler 

 and the ovary is not segmented. 



The development of Nematodes begins in some cases only 

 after the eggs have been laid : such eggs are almost always provided 

 with thick shells. In other cases the earlier stages, and sometimes 

 even considerably more advanced stages, are passed through in 

 the uterus of the mother, and a few (Triohinella spiralis, species of 



