ANATOMY OF MEDUSA 



273 



in communication, there is a community of nutrition among 

 the members of the colony. But a hydranth has nothing 



Fig. 58. 



Longitudinal section through a hydranth of Obelia. 

 geniculata ; m, mouth ; hy, placed in the cavity of 

 the hypostome ; gv, gastro-vascular cavity ; ec, 

 ectoderm ; en, endoderm ; ing, mesogloea ; nc, nemato- 

 cysts on the tentacles ; en 1 , large vacuolated endoderm 

 of the solid tentacle ; ht, hydrotheca. 



to do with reproduction, except that it gives rise to a bud 

 in prolongation of the colony. (For it must be understood 

 that although the apparent stem and flowers are called by 

 different names they are not organically different structures. 



