CLASS OF CESTOIDS OE T^NOIDS. 



503 



most other vertebrata.* The nematoids (helminthes) have the 

 body cylindrical, and attenuated 

 at the two extremities ; ex- 

 teriorly they greatly resemble 

 earth-worms, and also, as in the 

 annelides, their intestinal canal 

 is simple, and extended from 

 one extremity of the body to the 

 other ; but their nervous system 

 is rudimentary, and their blood 

 is colourless. 



The principal genera of this 

 class are, the ascarides (Fig. 

 178), the strongyli, and the 

 filaria. 



CLASS OF CESTOIDS OK 

 T^NOIDS. 



591. The cestoids are also 

 intestinal worms, but they 

 differ from the nematoids (hel- 

 minthes) greatly in their form 

 and mode of organization, and 

 more resemble the turbellaria. 

 They have the body flattened, 

 much elongated, and divided in- 

 to a great number of segments, 

 which gives them the appear- 

 ance of a long ribbon folded 

 transversely. Their nervous 

 system is rudimentary, and 

 their intestinal canal appears to 

 be replaced by two longitudinal 

 vessels occupying the sides of 

 the body. They are hermaphro- 

 dite, and each ring (segment) 

 of their body possesses a com- 

 plete reproductory apparatus, 

 belongs to this division (Fig. 531). 



* It would seem from the researches of Van Beneden and others, that 

 these parasitical animals are introduced into the bodies of others from with- 

 out, in the condition of ova in fact, and that their future development 

 depends on their reaching the habitat suited to them. R. K. 



Fig. 531. Tape Worm, Taenia. 

 The tcenia, or solitary worm, 



