154 



ZOOLOGY 



SECT. 



But the most characteristic anatomical feature of the group is 

 the structure of the sense-organs, which are club-shaped bodies 

 (Figs. 112 and 113, tc) consisting of an outer layer of ectoderm 



I.Pel'aeue 



2. G I o sso c o dor> 



V. 



FIG. 112.^Two Trachy medusae, dr. c. circular canal; J/OH. gonad ; mub. maiiubrium ; mtk. 

 mouth ; rail. c. radial canal ; re. c. recurrent canal ; t. tentacle ; tc. tentacul'ocyst ; tg. tongue ; 

 vl. velum. (After Haeckel.) 



rad.c 



mth 

 l.Cunarcha 



2.Polycol|3a 



Fio. 113. Two XVarcoxnedusJe, -1 in vertical section, rton. gonad; mnb. rnanubrium ; mtlt. 

 mouth ; pr. peronium ; rad.r. radial canal ; t. tentacle ; tc. tentaculocyst ; t.r. tentacle-root ; 

 v.l. velum. (After Haeckel ) 



enclosing a central axis of endoderm cells (Fig. 114): they have, 

 therefore, the structure of tentacles. They contain one or more 

 lithites, which are always derived from the endoderm. To 



