The female reproductive apparatus. of the Crustacea, in its, highest state of complication, consists of an ovary, an oviduct, and copulatory pouches.
in their course. to a kind of sac (c), the neck of which extends to the exterior of the ani mal's body (d); there is one of these on each side, and they are known by the name. of the copulatory pouches. It is into these reser voirs that the male pours the fecundating fluid, which is here stored up and applied to the ova as they pass in succession along and out of the oviducts. These after a course, which is never long, terminateat the vulvw, openings formed in the sternal pieces of the segment which supports the third pair of ambulatory extremities .
The Anomoura and Macroura have no copu latory pouches, and their vulvw are situated on the basilar joint of the ambulatory ex tremities of the third pair. The mode in which fecundation is acconiplished in these genera is consequently much less apparent. than in the Brachyura. Many writers are of opinion that this operation takes place in the interior of the ovaries, a process that appears by no means feasible on account of the inequality of development of the ova, which is such, that the last of them are not in being even long after the first have been ex pelled. It would perhaps be. more correct to suppose that fecundation does not take place till after the ova are laid, which we know to be the case among the Batrachia and the greater number of Fishes.
The female Crustacean does not abandon her eggs after their extrusion. Those of the pods preserve them under their abdomen by means of the abdominal extremities modified in their structure (fig. 390 and 433); the Edriophthalmia, again, keep them under their thorax by means of the belliform appendages of the extremities belonging to this region (fig. 436); whilst the inferior genera, such as the Eutomostraca, &c. have pended to the external orifices either horny tubes or a 'The ovaries in the Decapoda brachyura resem ble four cylindrical tubes (a, b, fig. 434) placed longitudinally in the thorax, and divided into two symmetrical pairs, each . opening into a distinct oviduct, yet communicating vvith one another by a transverse canal (a'), and by the intimate union of the two posterior tubes in a portion of their length (b1). The ovi ducts,, as well as the ovaries„ are of a whitish colour; they a.re s)iort, and become united pair of membranous sacs which contain and tninsport them from place to place. These
varieties in the accessory organs of gene ration, are in many cases sufficient to distin guish the sexes : thus, among the Decapoda brachyura, the females are known at a glance by their wider abdomen, which is sometimes of such dimensions as to cover almost the whole sternum. Sometimes these sexual diffe rences extend to the antennm and to various other organs; sometimes it even influences the size, and occasionally, as we have said, the general external conformation is modified to such a degree, that the male and the female of one and the same species have been taken as types of two distinct genera. There are some species of which the females only are as yet known to naturalists.
The ovum appears to be formed in the walls of the ovary, from whence it is detached when it has attained a certain size, and falls into the cavity of the organ. We have already stated in what manner it is expelled, and in what mode fecundation is accomplished in its pas sage through the oviducts, or afler its extru sion. The distinguished German naturalist, Ratlike, [has given particular attention to the divers phases of the evolution of the egg of the Astacus fluviatilis, as well before as after its escape from the ovary and oviduct; and we believe we cannot conclude this article more satisfactorily than by presenting our readers with a simple and brief analysis of his work.* The first and earliest form under which the ovum meets the eye in the ovary is that of a transparent vesicle, its walls of extreme te nuity, and filled with a watery fluid. This is the vesicle of Purkinje. By-and-by there is another membmnous and very thin envelope formed all round this vesicle, and in the minute interval that separates the two coverings there is a second fluid deposited, transparent like the other at first, but soon becoming opaque, whitish, and viscid; this is the vitellus or yolk. As this increases in size, the vesicle of Purkinje, which still preserves its first dimen sions, quits the centre, and goes to be attached to the circumference, which, at last, it almost touches at one point. During this time the vitellus or yolk is eontinually declining in transparency, on account of the formation of an infinity of globules, which, at length, transform it into a viscid mass of a deep brown colour.