CCELENTERATA. 



175 



(ctenophora = comb-bearers). There is no proboscis, the 

 wide mouth, with an ectodermal oesophagus, being at one 

 pole of the body and leading to a digestive tract which 



m 



FIG. 22. Diagram of a Ctenophore. c, rows of combs ; g, branches of digest- 

 ive tract; i, "intestine" ; m, mouth; o, oesophagus; s, sensory plate ; t, ten- 

 tacle; tc, tentacle sheath; y, cesophageal vessel. 



branches again and again (g), so that at last a portion 

 underlies each row of combs. There are no nettle-cells in 

 these forms and there never occurs any alternation of 



