PEIMARY DIVISIONS AND CLASSES. 207 



and which have always from five to seven pairs of limbs 

 adapted for locomotion.* 



Fig. 152. The Leech. 



The division of vermes or worms ought to comprise also 

 several very distinct types. There is first the annelides 



. Fig. 153. Nereis. 



(Fig.152), whose ganglionary system is quite distinct through- 

 out its whole length, with red blood generally circulating in 



Fig. 154. Rotifera. 



a very complex vascular system, in which the respiration almost 

 always takes place in a well-developed branchial apparatus, 



Fig. 155. Ascaris. 



* It has been known for some years that the cirrhipides, which had been 

 formed into a particular class, ought to be restored to the class Crustacea. 



