50 ANTHOZOA. 



general mass of the Alcyon, which in this way derives its 

 nourishment from the numerous sources of supply dis- 

 tributed over its surface. 



FlG. 33. FIGURE OF POLYPES OF ALCYOX. 



The Polypes that are thus protruded will be found, on 

 examination, to differ very materially in their structure 

 from the Hydras described in the preceding chapter. In 

 the Anthozoa the Polypes, when expanded, are found to 

 have eight hollow tentacles, the margins of which are 

 fringed by a triple row of minute fleshy papillae. 



These tentacles surround a central orifice, which is the 

 mouth. Internally, we may perceive that each Polype is 

 furnished with a distinct stomach, suspended in the 

 centre of its body, not simply excavated in the gelatinous 

 substance. The space between this stomach and the 

 walls of the Polype is divided into compartments by 

 membranous partitions, whereby the stomach is sus- 

 pended and retained in its position. These differences 

 of structure, which are sufficiently evident, at once enable 

 us to distinguish the Hydrozoa from the Anthozoic 

 Zoophytes. 



Madrepores. It is evident that the Alcyons de- 

 scribed above must necessarily be of very limited 

 dimensions, else from the general softness of their 

 bodies, they would be overwhelmed by their own 

 weight. If, therefore, animals of similar organization 



