4 CORALS AND CORAL LS LANDS. 



aster consists of a tinted disk bordered with one or more series 

 of petals. And, in exact analogy, the polyp flower, in its most 

 common form, has a disk fringed around with petal-like organs 

 called tentacles. Below the disk, in contrast with the slender 

 pedicel in the ordinary plant, there is a stout cylindrical pedicel 

 or body, often as broad as the disk itself, and sometimes not 

 much longer, which contains the stomach and internal cavity of 

 the polyp ; and the mouth, which opens into the stomach, is at 

 the centre of the disk. Here then the flower-animal and the 

 garden-flower diverge in character, the difference being required 

 by the different modes of nutrition and other characteristics in 

 the two kingdoms of nature. The coral polyp is as much an 

 animal as a cat or a dog. 



The figures of the frontispiece, and others on pages 6, 7, 

 9, sustain well the description here given, and afford some idea 

 also of the diversity of form among them. 



The prominent subdivisions of polyps here recognized are the 

 following : — 



I. AcTiNoiD Polyps. — Related to the Actinia, or vSea- 

 anemone, in tentacles and interior structure, and having, as in 

 them, the number of tentacles and interior septa a multiple 

 of six. The name Actinia is from the Greek ray. 



II. CvATHOPHYLLOiu 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 fea- 

 ture of the Alcyonoids. The Cyathophylloids were the earliest 

 of polyps, and the most abundant species in Paleozoic time. 



HI. Alcyonoid Polyps. — Having eight fringed tentacles, 

 and other characters mentioned beyond ; as the Gorgonix and 

 Alcyonia. 



