ACANTHOCEPHALA. 385 



SUB-SECTION X. 

 THE ORDER OF ACANTHOCEPHALA ou SPINE-HEADED WORMS. 



THE worms included in this group are internal parasites 

 which are without perceptible segments, and with no 



FIG. 520. 



Spiue-headed Worm, Echinorltyncus gigas, Gcze. 



alimentary canal, and which adhere to the intestines in 

 which they live by means of a proboscis armed with 

 spines. One species (Echinorhyncus gigas\ found in 

 the hog, is eighteen inches long. 



SUB-SECTION XI. 

 THE ORDER OF NEMATOIDEA OK THREAD-LIKE WORMS. 



THE name Nematoidea comes from neina, a thread, 

 and eidoft, appearance, and is given to the worms of this 

 order because, in general, they are long, slender, and more 

 or less thread-like. 



Their covering or integument is dense, and does not 

 exhibit segments. 



This group is about the same as that named Coelel- 

 mintha by authors. 



The Nematoids are parasitic in various animals. Some 

 kinds, as the Round-worms (Ascaris) and Thread-worms 

 (Oxyuris) inhabit the human intestines; Strongylus lives 

 in the kidneys of the pig. Filaricu burrows in the 

 flesh of man in warm climates, and attains the length of 

 17 



