CORAL AND CORAL MAKERS. 21 



them, the number of tentacles and interior septa a multiple of 

 six. The name Actinia is from the Greek ray. 



II. Cyathophylloid Polyps. — Like the Actinoids in tenta- 

 cles and interior structure, except that the number of tentacles 

 and interior septa is a multiple of four. Ludwig and De 

 Pourtales state that the number in the earliest young state is 

 six, and that therefore the fundamental ratio is the same as in 

 the Actinoids ; and that they pass from this ratio by develop- 

 ments of tentacles and septa more rapidly on one side than the 

 opposite, and in such a manner that the number becomes after 

 the first stage a multiple of four. The Cyathophylloid polyps 

 hence combine this characteristic of the Actinoids with one 

 feature of the Alcyonoids. The Cyathophylloids were the ear- 

 liest of polyps, and the most abundant species in Paleozoic 

 time. 



III. Alcyonoid Polyps. — Having eight fringed tentacles, 

 and other characters mentioned beyond ; as the Gorgonise and 

 Alcyonia. 



I. ACTINOID POLYPS. 



The highest of Actinoid Polyps are those of the Actinia 

 tribe — the species that secrete no coral to clog vital action 

 and prevent all locomotion. The details of structure may be 

 best described from the Actinia or Sea-anemone, and after- 

 ward the distinguishing characters of the coral -making polyps 

 may be mentioned. In external aspect and in internal charac- 

 ters all are essentially identical. 



L NON-CORAL-MAKING POLYPS. 



As the figures on the frontispiece, and also the following, 

 show, the external parts of an Actinia are — a subcylindrical 



