194 



THE INVERTEBRATA 



The Ctenophora, apart from certain aberrant forms, are globular, 

 pelagic, transparent animals living in the surface waters of the sea. 

 They are usually classed with the Coelenterata, but they differ from 

 other members of that phylum in several important respects, notably 

 in the entire absence of nematocysts. 



Two British forms are easily procurable, Pleurohrachia pileus and 

 Hormiphoraplumosa. Pleurohrachia pileus is about the size of a small 



Fig, 144. Hormiphora pliimosa. After Chun. Side view. M. mouth leading 

 via stomodaeum into infundibulum ; ab.p. aboral pole with sense organ ; 

 ab.fu. aboral funnel of infundibulum ; pa.can. paragastric canal running to- 

 wards oral pole; 8, one of the eight meridional comb plates; ca. one of the 

 eight canals running towards 8; tn.po. a tentacular pouch; tn. a tentacle; 

 gel. gelatinous material. 



hazel nut, while Hormiphora plumosa (Fig. 144) is rather smaller. 

 They are transparent and ovoid. At one pole is the mouth; the only 

 other openings into the alimentary canal are two small pores near the 

 sense organ. At the other pole is the sense organ marked as a small 



