586 THE INVERTEBRATA 



folds, known as the genital pleurae because when they are present the 

 gonads lie in them. Behind this branchiogenital region the trunk 

 becomes more cylindrical and tapers gradually, as the abdominal 

 region, to the anm^ which is terminal. 



drk. 



Fig. 438. A Dolichoglossus kozoalevskii, x i. From Spengel. 

 col. collar; M. mouth; ^ro. proboscis; sit. gill slits; trk. trunk. 



The proboscis and collar are used in burrowing. They are distended 

 by the taking in of water by the action of cilia in the tubes leading to 

 the pores, and contracted by muscles in the body wall, the water being 

 thus driven out. The proboscis first enters the mud and the collar 



