wn ZOOLOGY. 



minate in a bifurcated and articulated tail, by which they 

 aitarh themselves to bodies on which they wish to rest; 

 finally, two small red points seem to represent the eyes. 



These animalcules swim with 

 the greatest vivacity, and lay 

 oval eggs. 



588. Other animalcules, 

 called branchions, resemble 

 the rotifera in the general 

 modeof their organization, but 

 merit notice by reason of a 

 sort of carapace or shell with 

 which their body is covered. 

 In several of these small 

 beings the shell or covering is 

 even bivalve, and recals very 

 much that of certain crusta- 

 cea, such as the cypris and 

 daplmia. 



CLASS OF TUBBELLABIA. 



589. This class ought 

 lo comprise a certain number 

 of vermes, whose body, more 

 F '- r Hi. Douve or less compressed, presents 



(Fa^-iola Hepatica). \. 



scarcely any traces ot annu- 



lation, and is covered with extremely fine vibratile cilia. 

 In general they have no anus, and their digestive apparatus is 

 ramified, and terminates in a culdesac; their nervous sy.-trm 

 is composed of two lateral cords, terminating anteriorly in a 

 pair of cerebroid ganglions, and they have distinctly-formed 

 bloodvessels. Some, as the nemertes and the planaria, live 

 in water. Others, as the douve (Fasciola Hepatica, Fig. 444), 

 are parasites, and live in the interior of other animals. 



CLASS OF HELMINTHES, OB NEMATO1DS. 



590. This division is composed of a part of those animals 

 sometimes called intestinal worms, by reason of their living 

 generally as parasites in the intestinal canal of man and of 

 several other rertebrata. The nematoi'ds (helminthes) have the 



