I08 THE OCEAN WORLD. 



Stem and branches are alike in texture : slender, homy, 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 inter- 

 ruptions 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 

 polyps 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 plam or 

 tubulous perforation in the centre, through which the connection 

 between the individual polyps and the common medullary substance 

 is retained. Besides the polyps, there are found at certain seasons 

 a number of reproductive bodies, called gotiophores, readily distiri- 

 guished from the polyps by their size, and the irregularity of their 

 distribution, which are destined to contain and mature the ovules. 



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

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

 receiving the food and the expulsion of the residuum of digestion, 

 as will be so easily seen in the common sea anemone. 



In nearly all the Ccelenterata the sexes are separate ; the genera- 

 tion is sometimes sexual ; but these beings multiply also_ by what 

 zoologists call gemmation, or budding. Some are provided with 

 supposed organs of sense ; many of the swimming forms having eye- 

 like marginal bodies — a progress in organisation as compared with 

 the animals which have hitherto engaged our attention. Vibratile 

 cilia often cover the entire surface of the Polyps, and their tegumen- 

 tary system is richly supplied with thread cells. 



These general remarks may appear obscure and insufficient to 

 the large number of our readers. They are necessarily so ; they are 

 at best but generalities upon an interesting group of animals. We 

 (luit them, trusting to make the special study of the several classes 

 we shall have to describe more interesting. 



The sub-kingdom Ccelenterata naturally divides itself into two 

 groups — that of the Hydrozoa, and that of the Adinozoa. The 

 pretty fresh-water Hydra will serve as an example of the first, and 

 the common sea anemone of the second group. The essential 

 difference between the two is, that in the former the stomachal 

 cavity is not separated from the general cavity of the body, and the 

 reproductive buds are external; while in the latter the stomachal 

 cavity is let down, as it were, as a partially-closed sac, into the 

 general cavity of the body ; and the reproductive buds make their 

 appearance between the walls of the general cavity and the alimentary 



