66 



VERTEBRATE ZOOLOGY 



They depend for food upon minute organic particles that come to them 

 in the water and may be swept into the mouth by means of the ciliated 

 grooves of the tentacles. Many other sessile animals have a similar 

 feeding mechanism. In fact there are few fixed forms that do not 

 have feeding adaptations of this sort. Like the colonial ascidians, 



np 



PP 



FIG. 38. Sectional view of Cephalodiscus. a, anus; bd, bud on stolon ()', 

 cc, collar cavity; dl, dorsal tentacles; g, gonad; i, intestine; M, mouth; nc, noto- 

 chord; np, neural plate of collar region; p, proboscis; ph, pharynx; phc, pharyngea.1 

 cleft or gill slit; pp, proboscis pore; pc, proboscis cavity; S, stomach. (Redrawn 

 after Patten.) 



Cephalodiscus reproduces by asexual budding as well as by eggs 

 and sperm. 



Rhdbdopleura (Figs. 39 and 40), a genus with about four known 

 species of minute tubicolous forms, is obtained by deep-sea dredging. 

 They are of microscopic size, scarcely more than one-tenth of a mil- 



