268 THE INVERTEBRATA 



blunt teeth, which cannot pierce the human skin; a single pair of 

 coeca in the mid gut. 



This leech is carnivorous, devouring earthworms, aquatic larvae of 

 insects, tadpoles and small fish. The land leeches of the tropics, of 

 which Haemadtpsa may serve as an example, live in forests and swamps 

 and, mounted on leaves and branches, wait until a suitable mam- 

 malian prey presents itself. 



Class GEPHYREA 

 Annelida which have lost their segmentation partly or completely : 

 with a spacious coelomic cavity. 



The Gephyrea are annelids of comparatively large size and burrow- 

 ing habits. They are divided into two orders, the Echiuroidea and the 



an.-^ ^an.v. 



Fig, 197. Echiurus. Ventral view of larva to show segmentation of posterior 

 end. After Hatschek. an. anus; an.v. anal vesicle; M. mouth; mt. metatroch; 

 nep. nephridium; prt. prototroch; sep. septa of transitory segments; v.n.c. 

 ventral nerve cord. 



Sipunculoidea, which differ in the extent to which they depart from 

 the chaetopod type. 



Order Echiuroidea, with a well-developed prostomium, a terminal 

 anus, a single pair of ventral chaetae, sometimes several pairs of 

 segmental organs, and in Echiurus a trochosphere larva in which 

 develop fifteen pairs of mesoblastic somites (Fig. 197). 



Echiurus, with a spoon-shaped prostomium, two pairs of segmental 

 organs and a trochosphere larva. 



Bonellia (Fig. 198 A, B), with enormously elongated prostomial 

 proboscis bifurcated at end and extremely mobile ; a single segmental 

 organ (brown tube); the female is the normal individual and the 

 males are reduced to small ciliated organisms, like a turbellarian, 

 which live in the segmental organ of the female = 



