POLYPIFEEA. 117 



says, " there is but one life and one plan of development in the whole 

 mass, and this depends, not on the Polypi, which are but secondary, 

 and often deciduous parts, but on the general fleshy substance of the 

 body ;"* " the ramifications," says Dr. Johnston, " being disposed in a 

 variety of elegant plant-like forms. The stem and branches are alike 

 in texture : slender, horny, fistular, and almost always jointed at short 

 and regular intervals, the joint being a mere break in the continuity 

 of the sheath, without any character of a proper hinge, and formed by 

 regular periodical interruptions in the growth of the polypidoms. 

 Along the sides of these, or at their extremities, we find the denticles 

 or cup-like cells of the polypi arranged in a determinate order, either 

 sessile or elevated on a stalk." Near the base of each of these there 

 is a partition or diaphragm, on which the body of the polyps rests, 

 with a plain or tubulous perforation in the centre, through which the 

 connection between the individual polyps and the common medullary 

 pulp is retrained. Besides the cells, there are found at certain seasons 

 a larger sort of vesicle, readily distinguished from the others by their 

 size, and the irregularity of their distribution, which are destined to 

 contain and maturate the ovules. 



With these animals the digestive tube is very simple, and presents 

 only one distinct orifice; the same opening serving at once for re- 

 ceiving the food and the expulsion of the residuum of digestion. This 

 is one of Nature's economies, which it is not for us to dispute : we 

 must record it without further remark. 



In nearly all the Polyps the sexes are separate ; the generation is 

 sometimes sexual ; but these beings multiply also by what the zoolo- 

 gists call gemmation, or buds. They are provided with organs of the 

 senses ; nearly all of them have eyes an immense progress in organ- 

 ization as compared with the animals which have hitherto engaged our 

 attention. Their respiration is effected by the skin another instance 

 of the economy of Nature. The apparatus of their circulation is indis- 

 tinct, but they have a nourishing fluid analogous to the blood in 

 vertebrated animals. Yibratile cilia and stinging hairs often cover 

 the entire surface of the Polyps. 



These general remarks may appear obscure and insufficient to the 

 larger number of our readers. They are necessarily so; they are 

 generalities upon animals very little known, even to naturalists. We 

 * " Outlines of Comparative Anatomy." 



