The Sepia, among the Decapodous Cephalo pods, manifests in its generative, as in its prehensory and testaceous organs, a near affinity to the Tetrabranchiate order, while the form of the female apparatus in the Octopods more closely corresponds, on the other hand, with the same parts in the Oviparous Cartilaginous Fishes. The ovarium in both tribes is a single organ, situated at the bottom of the pallial sac, and consisting of a capsule and ovisacs di versely attached to its internal surface.
The ovisacs are proportionally larger in the Decapods than in the Octopods. In the Cuttle-fish they are extremely numerous, and are appended by long and slender pedicles to a longitudinal fold of membrane extending into the ovarian cavity, from the dorsal aspect of the sac. The plicze of the internal glan dular surface of the ovisacs or calyces are disposed in a reticulate manner, forming cor responding light-coloured opake lines on the external surface,which, being contrasted against the dark-brown tint of the contained ovum shining through the transparent areolar space, occasions the beautiful and characteristic ex terior reticulate markings of the undischarged ovisacs.
In the Genus Rossia, from which the sub joined illustration of the Decapodous type of the female organs is taken (fig. 239), the ovisacs have the same structure and mode of attachment as in Sepia, but they are rela tively of double the size and fewer in num ber. In the specimen which we dissected, we found the greater part of the ovisacs con taining the ovum in various stages of deve lopment, as at a, a. One was in the act of shedding the ovum, as at b, ; others were discharged, collapsed, and shrivelled, and in progress of absorption, as at c, c. The pa rietes of the ovarium consist of a thin and almost transparent membrane, which is con tinued forwards to form the oviduct (d, d). This canal commences in the Cuttle-fish by a round aperture, about a third of an inch in diameter, immediately beyond which it dilates, and continues forwards of the same thin and membranous structure to within an inch of its extremity, where, as in the Nautilus, its pa rietes are suddenly thickened by the develop ment of a number of broad, close-set, glan dular laminw. The chief difference between the Sepia and the Nautilus obtains in the greater extent of the membranous part* of the oviduct in the former.
In the Rossia the oviduct (d) differs only in greater relative width : the terminal gland (e) is composed of two lateral semioval groups of transverse glandular lamellae, each group being divided by a middle longitudinal groove; the oviduct was contracted immediately before opening into the interspace of the glands, and a deep but narrow groove, which is probably dilated during the passage of the ova, was continued between the two groups of' lamellm to the termination of the oviduct. This was situated towards the left side and behind the orifices of the nidamental glands.
The female organs of' the Sepiola present the same structure as in Sepia and Rossia, but the single oviduct is relatively wider than in the latter genus, the ova being of remarkably large size. In the Calamary the ovary is more elongated, and th e ovisacs and ova are relatively smaller than in any of the above genera. In the common species ( Loligo vulgaris ) the oviduct is single, but narrower, and more elongated than in the Sepia, and, like the vas deferens in the male, it is disposed in convolutions ; its terminal gland is relatively larger and longer; and the detached nidamental glands are correspond ingly restricted to a smaller development.
In the great Sagittated Calamary, which is not uncommon on our north-western shores, we found in a large specimen taken before the ben-inning of the breeding season, that the ovrducts commenced by separate apertures about two inches apart from the anterior sur face of the great ovarian bag, and were imme diately disposed in sixteen short transverse folds, beyond which they continued straight to the terminal ovarian gland. The whole length of each oviduct was two inches ; the convoluted portion occupying one inch ; the straight and glandular parts each half an inch. Monro, in his anatomy of this species of Loligo, conjectured that the glan dular appendages of the biliary ducts, of which he gave a figure, were the ova : of the. oviducts and nidamental glands he had no knowledge. The latter parts are situated external to the terminations of the oviducts; they are of a narrow, elongated, flattened form, about one inch and a half in length, with a wide cavity for moulding the secretion of the two lateral series of glandular laminm.