CORALS. 



39 



obtained, having been conveyed into the stomach of the Polype that caught 

 it, and digested there, is absorbed into the general mass of the Alcyon, which 



in this way derives its nourishment 

 from the numerous sources of supply 

 distributed over its surface. 



The Polypes that are thus pro- 

 truded will be found, on examina- 

 tion, to differ very materially in their 

 structure from the Hydras described 

 in the preceding chapter. In the 

 Anthozoa the Polypes, when ex- 



FIG. 32. ALC\ON. 



panded, 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 cen- 

 tral 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 be- 

 tween this stomach and the walls of the Polype is divided into compartments 

 by membranous partitions, whereby the stomach is suspended 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 described 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 



