TYPE ANNELIDA. 



207 



metamere, and leads in many forms into a strongly muscular, 

 usually protrusible pharynx provided with chitiuous teeth. 

 Upon the pharynx follows the usually straight intestine which 

 opens to the exterior at the posterior extremity of the body. 

 In Capitella and the allied genera, as well as in certain mem- 

 bers of the family Eunicidse, an accessory intestine lies ven- 

 trally to the principal one, into which it opens either both 

 anteriorly and posteriorly or else anteriorly alone. This ac- 



U y dm-db 



u n urn ub c 



FIG. 99. DIAGRAM OF TRANSVERSE SECTION OF ANNELID (combination of 



figures by LANG and EHLERS). 



br = brancliia. 



c = cirrus. 

 cm = circular muscles. 



co = cosloni. 



db = dorsal blood-vessel. 

 dm = dorsal mesentery. 

 hy = hypodermis. 



i = intestine. 



Im = longitudinal muscles. 

 ne = nephridium. 

 ov = ovary. 

 p = parapodium. 

 ub = ventral blood-vessel. 

 um = ventral mesentery. 



un ventral nerve-cord. 



cessory intestine is ciliated and seems never to contain food- 

 matter ; it has been considered to be respiratory in function 

 and seems to be a special development of a ciliated groove 

 which runs along the ventral surface of the intestine in cer- 

 tain other forms. Ponch-like outgrowths of the intestine are 

 frequently present and may sometimes become essentially 

 glandular in function. In Hesione and in certain species of 

 Syllis pouches communicating with the anterior part of the 



