TYPE PROSOPYGIA. 



259 



ing as retractors, while the circular muscles are specially de- 

 veloped as a rule only around the mouth of the cup, which 

 may by their action be closed over the retracted tentacles. 

 A relatively spacious coalom, containing a colorless corpuscu- 

 lated haeinolyrnph is present, and is lined by flattened perito- 



ec 



en 



FIG. 115. DIAGRAM OF THE STRUCTURE OF Alcyonidium albidum (after 



PROUHO). 



a = aims. io = interteutacular organ. 



ce = ganglion. m = retractor muscle. 



co = cuilom. oi) = ovary 



ec = ectocyst. t = tentacles. 



en = endocyst. te = testis. 



neal cells, some of which bear tufts of cilia. The intestine 

 has a characteristic Y-shape (Fig. 116), its posterior portion 

 being prolonged backwards to form a c?ecal pouch, from the 

 extremity of which a band or plate, the funicidus (Fig. 116, /), 

 containing in some cases muscular fibres, and lined by perito- 

 neal cells, arises, and passes backwards to be inserted into 

 the ectocyst posteriorly. The anus (a), as already stated, 

 opens on the anterior surface of the body, outside the limits 

 of the lophophore, and between it and the mouth lies the 

 nerve-ganglion, which is frequently hollow and sends off 

 nerves to the various portions of the body 



