158 



A COURSE ON ZOOLOGY. 



proper degree of moisture is restored to them, they 

 again become endowed with the functions of life. 



PARASITIC WORMS OR HELMINTHES. 



Under this heading are classed the in\?stinal worms 

 formerly considered as zoophytes, but which certainly 

 present much greater analogies with the anarthropoda. 

 Their bodies are composed of rings, or rather segments, 

 arranged in linear series. They have no organs of 



FIG. 91. 



TAPE-WORM. 



locomotion, and sometimes no digestive apparatus, in 

 the latter cases they absorb through the skin the juices 

 w r ith which they nourish themselves ; they also respire 

 by the skin, for there is no special respiratory apparatus. 

 Intestinal worms are divided into three classes: 



1. Ribbon-like worms, or cestoidea. 



2. Round worms, or nematoidea. 



3. Flat worms, or trematoidea. 



