CNIDARIA 



85 



axial individual are developed in t.lie 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- 





-UtZ 



Fig. 39.— Older stage of development of the colony of Renilla (after E. B. Wilson). 

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



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

 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 entoderraal layers 

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

 quently degenerates, and which is apparently homologous to 



