ANATOMY AND PHYSIOLOGY OF ANNELIDS 103 



organs — tactile organs known as dorsal tentacles and ventral 

 " palps " and ej-es and taste organs. The tail segment, which 

 contains the anus, frequently bears a pair of tentacles which 

 are useful when the worm moves, as it often does, backward. 

 The lateral appendages of the more perfect annelids are 

 stout, fleshy, paired protuberances on each segment of the 

 trunk. These are covered with a thin skin to permit of ex- 

 change of gases with the water, and so they would l)e without 

 support were it not for great dark bristles, one of which lies 



Fig. 160. — Diagrammatic representation of pharynx of a carnivorous 

 Annelid, f;, brain ; k. jaw; ph, pharynx; vi, mouth; rl, retractors; pt, 

 protruders ; vt, extru.sihle part of pharynx; p, its papillie. A, pharynx 

 retracted. S, pliarynx protruded. luB,ct, retractors; pi, flexible part of 

 pharynx. After Lang. 



in the axis of each of the two main lobes of the appendage and 

 serves for the direct attachment of the muscles that move the 

 appendages. In addition, the appendage carries many finer 

 bristles (chatte, whence the name "chsetopod," applied to the 

 group to which Nereis belongs), and these are exceedingly 

 diverse in form in the different families of chsetopods. In 

 certain species the bristles cover and protect the bodj^ (Fig. 

 179). 



The organs of nutrition consist of a food-canal and its glands. 

 The food-canal usually begins in a mouth cavity at the hinder 

 end of which is a thick muscular pharynx, the entrance to which 

 is guarded by a pair of jaws made of the same substance as the 



