2. Animals having, in addition to the ovige rous apparatus, a glandular structure, the secretion of which is probably subservient to the fertility of the ova.
3. Ovigerous and impregnating organs, co existent in each individual, but the cooperation of two or more needful for mutual impregna tion.
4. The ovigerous and impregnating appa ratus existing in distinct individuals.
-Animals in which ovigcrous organs only have been distinctly recognized.
It would seem from the observations of Ehrenberg that some of the Polygastrica be long to this division, although the exact nature of the generative system in such species remains still a matter of uncertainty. In the Kolpoda Cucullus the spawn consists of a loose mass of ova, connected by delicate filaments, from which the young are gradually evolved after their extrusion from the parent animalcule, and some of the parenchymatous Entozoa appear to be similarly circumstanced.
In the Acalephw, at least in such as have been most attentively examined, the generative system conforms to the type at present under consideration. From the researches Of Geede and Eysenhardt it appears that the ovaria are four in number, disposed in a cruciform manner upon the dorsal aspect of the body or that which is opposite to the mouth. These ovaria, which at certain seasons of the year are re markably distended and often beautifully coloured, open into the interior of the stomach. The young Medusa are hatched in the ovaria, and afterwards escaping into the alimentary canals excavated in the substance of the body, acquire in that situation a very perfect state of development, and are ultimately excluded through the oral aperture, or in the lthizosto matous species through the ramified canals of the pedicle.
In the fleshy polypes (Actinim) the ovigerous system consists of long, convoluted filiform tubes, contained between the stomach and the parietes of the body, and separated by partitions which divide that space into compartments. These tubes are attached by a delicate mesen tery, and according to Nix open in an irregular manner into the digestive cavity, into which the ova escape. The period or mode in which the eggs are hatched is unknown, but that the young escape fully formed and in every point resembling their latent through the stomachal orifice is attested both by Diequemare and Blainville.*
The different forms of Echinodermata pre sent a similar simple arrangement of the gene rative apparatus. In the Asteriadre each ray is furnished with two clusters of short ovigerous tubes, which are closed at one extremity, but open at the other into a cavity common to each group. These organs open by a series of aper tures placed around the circumference of the mouth at the base of each ray. In the spring these ovaria are distended with eggs of ts reddish-brown colour, which are expelled in clusters and left upon the beach exposed to the influence of the sun, where they are ulti mately hatched.t The radiated type of structure is likewise manifest in the disposition of the generative organs of the Echinida: in these the ovaria are never single or simply bilobed, but are at least four in number, or, as is generally the case, five. Each ovigerous organ consists of a simple dilated sacculus, which at certain seasons is distended with ova, and at such times in some species, as in the edible Echinus, the eggs are sought after as an article of food. The ovaria open externally by a corresponding number of simple apertures, which are placed around the anal orifice when it is central, but otherwise are considerably removed from this point. Nothing analogous to a male apparatus has been detected in the Echinida. The eggs are deposited in spring in the recesses of rocks or among the focus which covers them ; and before they are hatched the young may be dis covered in the interior partially covered with a calcareous shell, the rest of the integument still remaining membranous.
The Holothuridm present in the elongated form of their bodies an evident approximation to the annu!ose type of structure, and a propor tionate concentration of the generative system ; in these we find but one ovary floating loosely in the visceral cavity, and composed of numerous very long cceca, which terminate by a single orifice placed on the median line, near the oral extremity of the animal.* The eggs when dis charged are connected into masses composed of long strings of ova, but the mode of their development is but little known.