CNIDARIA 



85 



axial individual are developed in the anterior part of the 

 polyp, and grow from in front backwards ; nevertheless they 

 are restricted, even in late stages, to the anterior parts of 

 the individual, whereas in most Alcyonaria the septa extend 

 as far as the posterior end of the body. On the other hand, 

 another wall is developed in Renilla by a transverse infold- 



■wz 





Fig. 33.— Older stage of development of the colony of 'RemWa (after E. B. Wilson). 

 J), terminal polyp ; z, terminal zooid ; mz, marginal 20oid; dz, dorsal zooid. 



ing of the entoderm from the posterior end of the body, tlie 

 so-called 'peduncular septum^ by means of which the gastral 

 cavity is divided into a ventral and a dorsal half. The 

 peduncular septum grows from behind forwards ; and since it 

 grows more actively at its lateral parts, its anterior margin 

 assumes a curved form. Between the two entodermal layers 

 of the peduncular septum is found a cell-mass which subse- 

 quently degenerates, and which is apparently homologous to 



