CNIDARIA 



85 



axial individual are developed in the anterioi* part of the 

 polyp, and grow from in front backwai^ds ; 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- 





-Wi 



Fig. 38. — Older stage of development of the colony of Renilla (after E. B. Wilson). 

 p, terminal polyp ; z, terminal zoöid ; mz, marginal 20öid; dz, dorsal zoöid. 



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

 so-called pednucniar 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 pai-ts, its anterior margin 

 assumes a curved form. Between the two entodei-mal layei\s 

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

 quently degenerates, and which is apparently homologous to 



