108 THE OCEAN WORLD. 
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 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 plain 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 gonophores, readily distin- 
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 Coelenterata 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 
quit 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 Aydrozoa, and that of the Actinozoa. 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 1s 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 
