CLASS OF CESTOIDS OR T^NIOIDS. 



459 



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. 

 155), the strongyli, and the 

 filaria. 



CLASS OF CESTOIDS OB 

 TJENI01DS. 



591. The cestoids are also 

 intestinal worms, but they 

 differ from the nemetoids (hel- 

 minthes) greatly in their form 

 and mode of organization, and 

 more resemble the turbellaria. 

 They have the body flattened, 

 much elongated, and divided 

 into a great number of seg- 

 ments, which gives them the 

 appearance of a long ribbon 

 folded transversely. Their ner- 

 vous system is rudimentary, 

 and their intestinal canal ap- 

 pears to be replaced by two 

 longitudinal vessels occupying 

 the sides of the body. They are 

 hermaphrodite, and each ring 

 (segment) of their body pos- 

 sesses a complete reproductory 

 apparatus. The tcenia or soli- 

 tary worm belongs to this division (Fig. 445). 



Tsenia. 



