NE MA THELMINTHES. 1 9 5 



causing ' ' gapes. " A remarkable large form , Ichthyonema, is found inside 

 sea-urchins. Various species of Tylenchits, especially T. devas- 

 tatrix and T, scandens (or T. tritici], destroy cereal and other crops 

 Various species of Heterodera (especially^, schachtii and H. radicicold) 

 infest the roots of many cultivated plants, e.g. turnip, radish, cabbage. 



Class NEMATOMORPHA. 



The Gordiidce (e.g. Gordius aqiiaticus the horse-hair worm) are so 

 different from true Nematodes that they must be ranked in a separate 

 class. There are no lateral lines. Three nerve-strands lie close 

 together in the mid ventral line. In the adult Gordius the mouth is 

 shut and the food canal is partly degenerate. The adult Gordiidce 

 usually live freely in fresh water ; larval forms occur in aquatic 

 molluscs, young insects, etc. ; later stages usually occur in carnivorous 

 insects, whence they emerge to become adult in the water. One form, 

 Nectonema agile, is marine. 



ClaSS ACANTHOCEPHALA. 



For a few genera, of which the best known is Echinorhynchus, 

 whose larvie live in Arthropods, and the adults in Vertebrates, a 

 special class, ACANTHOCEPHALA, has been established. They may 

 be placed beside Nematodes, but the relationship does not seem to be 

 very close. Mouth and gut are absent. The anterior end bears a 

 protrusible hooked proboscis. 



Echinorhynchus proteus of pike, minnow, trout, etc., larva in the 



Amphipod Gam mams pit lex. 



,, ' angii status of perch, larva in the Isopod Asclliis 



aquaticus. 



f rat, etc., larva in larval beetles (Blaps}. 



