THE SCOLECIDA. 



49 



tion must, I think, be answered in the affirmative. It is almost 

 the only system of organs in the Nematoidea which gives us a 

 definite zoological criterion, the condition of the nervous 

 system in these animals being still, notwithstanding the many 

 inquiries which have been made into the subject, a matter of 

 great doubt. 



Fi 



o- 22 



Fig. 22. — Oxyuris. — a. Mouth, h. Pharynx, c. Commencement of intestine, and d its 

 termination ; the intermediate portion is not figured, e. Genital aperture. /. 

 Opening of vessels, g. Their receptacle, h. One of the vessels, i. Cellular matter 

 enveloping them. A portion of one of the contractile vessels is represented above, 

 more highly magnified. 



In habit and feature, the Gordiacea, filiform parasites which 

 inhabit the bodies of insects, and leave their hosts only to breed, 

 resemble the Nematoidea so much that I can hardly doubt that 

 their systematic place must be close to that of the latter ; but 

 positive evidence is almost wanting on this head, the extant 

 accounts of the minute anatomy of these animals not having 

 received that kind of confirmation which is desirable. 



The structure of the Acanthoeejrfmla, comprising the for- 

 midable Echinorhynchus (Fig. 23) and its allies, is, on the other 

 hand, pretty clearly made out. They are vermiform parasites, 

 like the Txmiada, devoid of any mouth or alimentary canal, 

 but provided with a proboscis armed with recurved hooks. 

 The proboscis is supported within by a sort of rod-like handle, 

 whence a cord is continued, to which the reproductive organs 

 are attached. A single ganglion is seated in the "handle" 

 of the proboscis. Immediately beneath the integument lies 

 a series of reticulated canals containing a clear fluid, and it 



E 



