I So UNSEGMENTED "WORMS." 



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

 Various species of Heterodera (especially H. schachtii and H. radici- 

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



Class Gordiacea. 



The Gordiidce {e.g. Gordius aquaticus — the horse-hair worm) and 

 the Nectonemidse are so different from true Nematodes that they must 

 be ranked in a separate class. In the adult Gordius the mouth is shut 

 and the food canal is partly degenerate. The adults live freely in fresh 

 water ; there are two larval forms, the first in aquatic molluscs, young 

 insects, etc., the second in adult insects, fish, frog, etc. 



ClaSS ACANTHOCEPHALA. 



For a few genera, of which the best known is Eckinorhynchus, whose 

 larvae live in Arthropods, and the adults in Vertebrates, a special class, 

 Acanthocephala, has been established. We may provisionally 

 place these forms, of which there are several hundreds, beside Nema- 

 todes, but the relationship does not seem to be very close. Mouth 

 and gut are absent. The anterior end bears a protrusible hooked 

 proboscis. 



Eckinorhynchus proteus of pike, larva in the Amphipod Gammarus 

 pulex. 

 „ angustatus of perch, larva in the Isopod Asellus aqua- 



ticus. 

 i > gigos of pig, larva in young cockchafers. 



