(1600). All the Cephalopoda are dioecious; and the structure of the sexual organs both of the males and females is remarkable, inasmuch as it is peculiar to the class.

(1601). In the females, the ovarian receptacle is lodged at the bottom of the visceral sac (fig. 290, p, q), enclosed in a distinct peritoneal pouch. The ovary itself is a large bag, the walls of which are tolerably thick; and, on opening it, it is found to contain a bunch of vesicular bodies, attached by short vascular pedicles to a circumscribed portion of its internal surface (fig. 295, a.) These vesicles, the ovisacs or calyces, as they are called by comparative anatomists, are, in fact, the nidi wherein the ova are secreted; and if examined shortlybefore opposition commences, every one of them is seen to contain an ovum in a more or less advanced stage of development. In this condition the walls of the ovisacs are thick and spongy; and their lining membrane, which constitutes the vascular surface that really secretes the egg, presents a beautiful reticulate appearance.

(1602). If the contained ova be examined when nearly ripe for exclusion, each is found to be composed of a yelk or vitellus enclosed in a delicate vitelline membrane, and covered externally by a thicker investment, the chorion. When the ovum has attained complete maturity, the ovisac enclosing it becomes gradually thinned by absorption, and ultimately bursts, allowing the egg, now complete with the exception of its shell, to escape into the general cavity of the ovarium (c.) The oviduct (e) communicates immediately with the interior of the ovarium by a wide orifice, the dimensions of which are proportioned to the size of the mature ova. It is generally single; but in some genera, as Loligo and the Octopoda, the canal derived from the ovary soon divides into two (d, e.) The walls of the ovigerous duct are thin and membranous until near the external outlet, where they suddenly become thick and glandular, and, in many genera, surrounded with a very large laminated gland (f), through the centre of which the eggs have to pass before they issue from the body.

It is the gland last mentioned that secretes the external horny covering of the egg - a defence which seems to be deposited in successive layers upon the outer surface of the previously existing chorion, and, when completed, forms a thick flexible case made up of concentric lamellae of a dark-coloured corneous substance.

A. Generative organs of the female Cuttle fish. B. A bunch of eggs.

Fig.296. A. Generative organs of the female Cuttle-fish. B. A bunch of eggs.

(1603). After extrusion, the ova of the different families of Cephalopoda are found agglutinated and fastened together into masses of very diverse appearance. The eggs of the common Cuttle-fish, frequently found upon the shore, are not inaptly compared by those ignorant of their real nature to a bunch of black grapes, to which, indeed, they bear no very distant resemblance, being generally aggregated in large clusters, and fastened by long pedicles either to each other or to some foreign body (fig. 296.) The Argonaut carries its eggs, which are comparatively of small size, securely lodged in the recesses of its shell; while the ova of the Calamary, encased in numerous long gelatinous cylinders that conjointly contain many hundreds of eggs, are fixed to various submarine substances, and thus protected from casualties.

1. Male organs of the Cuttle fish (Sepia officinalis), seen from before.

Fig. 297. 1. Male organs of the Cuttle-fish (Sepia officinalis), seen from before: a, tunic enveloping the testis; b, body of the testicle; c, convolutions of the vas deferens; e, commencement of the Needhamian canal; d, pouch of Needham. In fig. 4 the same parts are represented as seen from behind, the testicle being removed in order to show the commencement of the vas deferens. 2 and 3 represent the spermatophores of the same animal, much magnified: a, the external sheath; b, inner cylinder containing the spermatic fluid; c, the ejaculatory apparatus. In fig. 3 the 8permatophore is shown in the act of discharging its contents.

The form and arrangement of these bunches are no doubt dependent upon the peculiar character of the terminal gland found in the oviduct of the parent, whereby the last covering to the ova is furnished.

(1604). Cuvier remarks that the male Poulpes must be less numerously met with than the female, as among the numerous specimens dissected by him scarcely one-fifth were of the former sex.

(1605). The various parts of the male generative apparatus are remarkably similar, both in structure and arrangement, to the corresponding portions of the sexual organs of the female. The testicle strikingly resembles the ovary both in its outward form and internal arrangement: like that viscus, it consists of a capacious membranous sac (fig. 298, 6); and on opening this there is found, attached to a small portion of its inner surface, a large bundle of branched caeca (a), in which no doubt the seminal fluid is elaborated. These strangely disposed seminigerous casca have apparently no proper excretory ducts; but the impregnating fluid secreted by them is, as it would seem, poured into the general cavity of the sac, exactly in the same manner as the ova in the other sex, and, being allowed to escape from this reservoir through a wide orifice (c), it enters the vas deferens. The canal last mentioned (d) is long, slender, and very tortuous, but after many convolutions it enters a wider canal (e), called by Cuvier vesicula seminalis, the interior of which is divided by imperfect septa; and, its texture being apparently muscular, this part of the excretory apparatus may possibly, by its contractions, expel the spermatic fluid from the body. On issuing from the seminal vesicle, the semen passes the extremity of an oblong gland (f), which Cuvier denominates the prostate: its structure is compact and granular; and it seems to be destined to furnish some accessory fluid subservient to impregnation. Having passed the prostate, the ejacu-latory duct communicates with a large muscular sacculus (g), the contents of which are very extraordinary.