FIG. 55. Diagrams illustrating the derivation of the medusa from 

 the hydranth. In the whole series of figures the ectoderm (ect) is dotted, 

 the endoderm (end] striated, and the mesogloea (msgl) black. 



A, longitudinal section of a simple polype, showing the tubular body 

 with enteric cavity (ent. cav), hypostome (hyp), mouth (nith\ and 

 tentacles (/). 



R 



