236 



SUBKINGDOM ARTICULATA. 



respiration is effected in some by gills and in others by the 

 whole surface of the body. Eyes are occasionally found. 

 Worms exist everywhere, in salt and fresh water, and on land, 

 and as parasites in man and other animals. 



Mostly aquatic. 

 Mostl (ROUND. 



I 



j WITHOUT CILIATED DISCS. Annulata, Nereis. 



I WITH CILIATED DISCS. Rotatoria, Rotifer. 



( WITH SPINES. Acanthocephalix, Echinorhynchus. 



i WITHOUT SPINES. Nematelminthes, Trichina. 



Platyelminthes, Tape-worm, etc. 



ORDER ANNULATA. 



General Characteristics. The Annulata have red 

 blood, a nervous system resembling that of insects, and the 

 alimentary canal extending the whole length of the body. 

 The body is elongated and the segments are distinctly 

 marked. Some are furnished with bristles, others are with- 

 out ; some have gills, others have none. 



fig. WU. 



Nereis pelagica. a, Male ; ft, Female. Natural size. 



The Nereidse have both bristles and gills arranged on 

 each side of the body, and the mouth is armed with 

 powerful jaws. 



The Serpulidse (see Fig. 393) are marine, with gill-tufts 

 around the head. Some live in calcareous tubes variously 

 contorted, adhering by the closed end to oyster-shells, etc., 

 but protruding from the open end brilliantly-colored, fan-like 

 appendages, with one dilated to close the shell when the 



