CCELENTERATA 



83 



for all the Ctenophora are hermaphroditic ; the germ-cells are 

 set free into the coelenteron. Entoderm lines the coslenteron, 



ad.c 



cede 



-no- 



■ ■■ 



1 



FlG. 71. Hormiphora plumosa. A, transverse section of one of the branches of 

 a tentacle; B, two adhesive cells and a sensory cell still more highly magnified. 

 ad.c, adhesive cells; cu, cuticula; nu, nucleus; s.c, sensory cell. (After Hert- 

 wig and Chun, from Parker and Haswell's Manual.) 



and the space between the ectoderm and the entoderm is filled 

 with mesenchyme. There is no alteration of generations in 

 this class, but the young animals often differ from the adult, 

 so that we may speak of them as larvae. In some species there 



FlG. 72. Cestus veneris, the Venus' girdle, showing its undulating form when 

 in motion; the mouth is at the center of the lower edge. (Drawn from a 

 Leuckart-Nitsche wall-chart, by the author; permission of Dr. C. Chun.) 



is the curious phenomenon that germ-cells are formed, and 

 mature at two distinct stages in the life of the individual, once 

 when it is young, and again when it is adult. 



The Ctenophora are most abundant in tropical waters and are 

 very beautiful, for the moving plates of cilia refract the light and 



