Page:Popular Science Monthly Volume 7.djvu/14

7 the column. These six compartments are made by as many radiating vertical plains, whose edges on the one side are in contact with the inner walls of the column, and the edges on the other side touch upon the outer walls of the stomach. Between these compartments are others of less capacity. It is noticeable that these are, in like manner, formed of vertical plains, of different widths; and, further, that they are only attached on one edge, and that to the inner walls of the



great column, that is to say, they do not connect with the stomach. To understand the relation of these different walls of the compartments to the entire structure, a glance at the diagram will suffice, when it is borne in mind that the transverse section, thus represented gives also a section of the inner cylindrical sac, or stomach.

The upright walls of these compartments which we have described are known in science by the name mesenteries. Of what use are they? The most obvious service they perform for the animal when erect is, as we think, the stiffening of the structure. And this is done at will, as if it were a sort of erectile tissue. Now, as the cardinal plains connect both the inner and the outer cylinder, that is, the stomach and the column, it will be seen that the efficiency in the direction of imparting strength is considerable. The column is by so much the more strengthened, as it has the more of these upright planes or septæ attached to it by one of their respective edges.

But it is in these compartments, and on the mesenteries themselves, that the origin of life for the actinia's progeny begins—for there the ova and the spermatozoa are found. On the mesentery-walls are borne in series certain reddish bands. These are the reproductive organs, and contain the ova and the spermatozoa. Generally actiniæ are what the botanists call diœcious; that is, the ova are found in an individual—that we may call the female; and the spermatozoa in one that we may in like manner call the male. As to the time, and even the method of propagation, mother actinia is very capricious, there being, so far as our observations may determine, no regularity, but at the right time doubtless, for her convenience, the actinia evicts her young. Usually these are discharged at the mouth.