METAZOA COELENTERA. 12T 



six simple tentacles. The mouth leads into an internal 

 bag l which communicates with the body cavity. The 

 latter is divided by six bilateral mesenteries. So far no 

 trace of biradial mesenteries has been discovered in the 

 young Antipathies, and these mesenteries we should 

 expect to find if this group were reduced descendants of 

 the Hexactiniae as some naturalists maintain. The 

 young Antipathes sends out fleshy prolongations from 

 the basal portion of its body and these bud other zoons,, 

 thus giving rise to a colony (No. 192). The bases of all 

 the zoons secrete a black horny stem or axis (No. 193,. 

 A. dissecta D. & M.) , which gives rigidity to the stalk. 

 This secretion is restricted to the "foot" of the zoons, 

 the body walls never taking part. We have seen that 

 this is also the case with some of the Alcyonaria, a group 

 in which Antipathes is sometimes placed. The posses- 

 sion, however, of six bilateral mesenteries seems to show 

 relationship with the Hexactiniae. 



Zoanthus solanderi Less. (No. 194), is a simple colony, 

 the members of which are connected by stolons. The 

 arrangement of the mesenteries is still essentially bi- 

 lateral. 



In Mammillifera ? (No. 195), the zoons arise from a 

 basal membrane and are of about the same height. 



Hexactiniae. The simple members of this group are- 

 illustrated by Halcampa chrys ant helium Gse. (No. 196), 

 which is a free-swimming animal. In its development it 

 passes through the Edwardsia stage of eight bilateral" 

 mesenteries, but when adult it possesses twelve biradial 1 

 mesenteries. 



The Actiniae next to be described are bilateral in the 



1 This organ is called in textbooks and manuals "oesophagus,"' 

 "stomach," "stomodaeum." According to Prof. E. B. Wilson it is 

 an ectodermic structure and has nothing to do with the stomach 

 structurally or functionally. It is homologous with a stomodaeum, 

 or, what is more probable, with a fused stomodaeum and procto- 

 daeum. We have called it simply a bag. 



