42 A Guide to the Zoological Collections m the 



I. NEMATHELMrNTHES NEMATODA. 



[^.(Llcstcrtt cEall-cas£ 46]. 



The Nematoda or Thread-worms are mostly parasitic 

 either in the intestine or in the blood-vessels of vertebrate 

 animals. The Nematoda usually have a complicated de- 

 velopment, and pass through larval stages in the tissues 

 of one or more intermediate hosts before they reach their 

 final sexually-mature growth in a permanent host. 



In the collection specimens of the following are exhibit- 

 ed : — Ascaris lumbricoides^ the common intestinal round- 

 worm, Ascaris from the intestine of the dugong, Trico- 

 cephalus dispar and Ankylostoma duodenale from the intes- 

 tine of man, and Filaria medinensis (the common guinea- 

 worm). The exhibited dissection of a large female of 

 Ascaris lumbricoides shows the nature of their internal 

 organization. 



2. NEMATHELMINTHES CH>ETOGNATHA- 



[SEcstern ®aU-ca0£ 46j. 

 The Chxtognatha include only the two genera Sagitta 

 and Spadella, small delicate worms found swimming free 

 at the surface of almost all seas. An enlarged drawing of 

 Sagitta is exhibited. 



3. NEMATHELMINTHES AOANTHOCEPHALA. 



[SJil^sttrn SEaU-ras£ 46]. 



The Acanthocephala include only the one genus Echin- 

 orhynchus, a parasitic round-worm, the head end of which 

 is armed with a thorny proboscis by means of which the 

 parasite maintains a firm hold on the wall of the gut of its 

 host. Like all parasites its organization is much degraded, 

 even a mouth and intestine being absent, the parasite as it 

 lies in the alimentary canal of its host being nourished by 

 simple absorption through the body-wall. 



A slightly enlarged drawing of Echinorhynchus gigas is 

 shown in Case 46. 



