Introduction to Animal Morphology. 149 



system. The anus has a round or pentagonal muscular 

 sphincter, into whose edges the longitudinal body 

 muscles are inserted. The pharynx is oval and 

 glandular, separated from the stomach by a sphincter, 

 surrounded at its origin by a moveablering of 10, 12, or 

 15 plates, five of which are usually notched or pierced 

 Synapta), radial, and five are inter-radial ; these re- 

 present the auricles of Echini. Five muscular bands 

 unite these plates, and 10-12 pyramidal bands arise 

 by their apices therefrom, and have their broad bases 

 inserted into the pharyngeal wall : they can draw 

 forwards the pharynx. The digestive canal is straight 

 or curved, attached by often uninterrupted mesenteries. 

 It sometimes ends in a cloaca directly above the anus. 

 In the intestine there may be 2-4 longitudinal folds, 

 possibly the extension of an absorbing apparatus. 

 The alimentary canal contains diatoms, foraminifers, 

 and sand. 



The dermis acts as a respiratory organ, so do the 



remarkable tree-like, long branching organs, ciliated 



within and without, which arise from the cloaca, and 



stretch in the body cavity towards the mouth. Water 



enters them from the cloaca, and passes into the body 



cavity from them by holes in the tips of the branches. 



-lungs are homologous to the inter-radial 



caeca riadoc. Water enters in other forms by 



inter-tentacular pores. The tree-like organs vary in 



forms they are joined to the wall of the 



somatic cavity by threads and even where the trees 



>ynai>ta , these threads remain appended 



to th< ith attached to their inner ends 



ciliated, slipper-like, or cornucopi.e-like organs, and 



communicating with the pseud-ha-mal system. Rarely 



