70 Invertebrata. 



organs or tubes opening laterally, one on each segment. 

 The egg-producing organs are very complex (fig. 42 A). 



Locomotion takes place by the suckers : the 

 hinder one being fixed, the animal elongates itself 

 and, fixing its front sucker, sets free the hinder one, 

 then shortening its body it proceeds in a similar manner. 

 Leeches can also swim, and when so progressing the 

 body becomes flattened by the contraction of vertical 

 muscular fibres which run from the dorsal to the ven- 

 tral surface, and then by undulating movements it 

 advances like a wavy ribbon. 



Medicinal leeches are principally imported from 

 Hunsrarv and Sardinia. 



CHAPTER XIII. 



NON-PARASITIC WORMS. 



CLASS VIII. Bristle-footed Worms (Chaetopoda). 

 The worms of this class re- 

 semble the leeches somewhat 

 in internal structure, but are 

 not parasitic, and all possess 

 a body cavity (absent in most 

 of the leeches) which con- 

 tains a fluid rich in minute 

 floating corpuscles. The 



class includes not only the D &Sn^l f 

 earth. worms and their fresh- S^df layJ" ''cj S 



Water allies With their SCantV plates; rf, segmental organ; A, 



J arterial, and z, venous blood- 



armament Of bristles, but also vessel ; g, intestine ; , ovary. 



the numerous species of bristle-bearing worms, of 



