208 UNSEGMENTED “WORMS.” 
and intestinal arteries of horse, causing aneurisms, colic, ete. The 
young forms are swallowed from stagnant water, bore from gut into 
arteries, become adult, return to gut, copulate and multiply. Various 
other species of S¢rongylus occur in sheep, cattle, etc. Of the genus 
Ascaris alone, over 200 species have been found in all types of Verte- 
brates ;—A. megalocephala in horses, A. /umbricordes in man, A. mystax 
in cats and dogs. Syngamus trachealis occurs in the trachea of birds, 
causing ‘‘gapes,” ¢.g. in poultry and pheasants. It pierces the wall 
of the trachea, and ‘‘ actually clenches the teeth with which its mouth 
is provided in the tracheal rings.” A remarkable large form, /chthyo- 
nema grayz, is found inside sea-urchins. Various species of Zylenchus, 
especially 7. devastatrix and T. scandens (or T. triticz), destroy cereal 
and other crops. Various species of Heterodera (especially H. schachtet 
and #. radiczcola) infest the roots of many cultivated plants, e.g. turnip, 
radish, cabbage. 
Class NEMATOMORPHA 
The Gordiide (e.g. Gordius aguaticus—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 Gordéus the mouth is 
shut and the food canal is partly degenerate. The adult Gordiide 
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 Achznorhynchus, 
whose larvee 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 used in boring in the intestinal wall of the 
host. In the minute swellings at the ends of the two much-branched 
excretory organs of Z. gégas, there are ciliated cells,—the only case 
known among Nematohelminthes. 
LEchinorhynchus proteus of pike, minnow, trout, etc., larva in the 
Amphipod Gammarus pulex. 
4 angustatus of perch, larva in the Isopod Ased/us 
aguaticus, 
ve moniliformis of rat, etc., larva in larval beetles 
(Blaps). 
of gigas of pig, larva in grubs of cockchafer, etc. 
