Male (pl. vi.).—The male organs consist of a testis, vas deferens, “prostate” gland, duct of the “prostate,” receptacle of spermatophores and penis. The testis (fig. 1 g) lies at the ab-oral end of the body, is large, irregularly oval in outline, and flattened. Its lower outline is concave, its upper convex. It is encased in a thin membrane attached on its anterior surface and uniting it below with the inner anterior surface of the mantle.
The vas deferens communicates with the capsule of the testis towards the upper end. Its commencement seems rather to be lost in the membrane than to have a well-marked opening. It is short but slender, and does not present the convolutions noticed in all descriptions of the male organs of Cephalopods that I have seen.
The vas deferens opens into a long, cylindrical vesicula seminalis, which leads to the “prostate” gland. The walls of the vesicula present well-marked transverse plicæ. Except that it narrows at either end, it is of about the same thickness throughout. It contains spermatozoa, which appear, when examined with the ¼-in. objective, to be simple straight rods. Though the walls of the vesicula appear to be thick and white, they are in reality thin and transparent, the white colour being caused by the spermatozoa. The plicæ may possibly be due to only partial distention.
The “prostate” gland (fig. 1 d; fig. 2) is a delicate tube, presenting marked convolutions, and having the appearance, when viewed on the posterior aspect, of a spiral coil. At the point where the vesicula seminalis enters it is dilated (3); then there is a strong convolution; then a slightly expanding tubular portion (2), which leads to a sac-like portion (1). Near the point where the vesicula enters is a small cœcal dilatation (4); and a similar dilatation is produced from the saccular portion from which the duct springs.
From the saccular portion, near the opening of this dilatation, springs the duct of the “prostate” (c). The wall of the “prostate” contains a network of branching and interlacing fibres.
The “prostate” gland differs from that of S. brevis, Owen, where it is described as an “oblong, blind, glandular sac.” Loligopsis ocellata, Owen, too, shows a blind sac with a single duct for ingress and egress. Indeed this character seems common, so far as I have been able to discover; but the species at present under notice differs widely in having the “prostate” a thickened tube or canal with ingress at one end and egress near the other.
The duct of the “prostate” (fig. 1 c) is slender, and has transparent walls. It leads to the receptacle of spermatophores, into which it opens near its upper end.
The receptacle of spermatophores (b) is a large sac with thin transparent walls, and is usually packed with spermatophores and loose spermatozoa. It opens by a wide mouth into the penis (a) of whose base it appears to be a simple dilatation.
The penis tapers gradually towards its opening, which has an uneven, almost fringed margin.
When in sitû the vesicula seminalis and the duct of the “prostate” lie parallel to each other along the receptacle of spermatophores, to whose walls and to each other they are held by a membranous connection. The whorls of the prostate are held together by similar connections, so closely as to require the exercise of the utmost care to sever them without injury to the organ. The vesicula, duct, and receptacle of spermatophores thus held together lie transversely to the axis of the testis.
Spermatophores (pl. vi., figs. 3–7).—A common length of the spermatophores is about 9 lines, but this is often exceeded. The shape varies somewhat, but the general outline is the same. One end is thickened, often club-shaped, or with a knob; from this end the spermatophore tapers, but as the opposite end is approached there is often a slight dilatation and the end is obtuse, never, so far as I have been able to observe, filamentous. The outer case is transparent and of tolerable consistency. The thick end is mainly occupied by a sac containing spermatozoa, which extends for varying distances, but seldom, if ever, half the length of the spermatophore. To this sac is attached a sponge-like body of definite though slightly varying shape, resembling the turned handle of an awl. This body fits into the spermatophoric tube like a piston. From it extends towards the thin end of the tube a flat spirally coiled thread enclosed in a transparent case. The thread may extend to the thin end of the spermatophore and be there attached, or it may extend nearly to the end and then be recurved, or it may not extend right to the end.
Professor Huxley (Anat. of Invertebrated Animals), on the authority of M. Milne-Edwards, describes the spring and the piston-like body as resembling the sponge of a gun with a spiral screw turned on the handle. I have carefully endeavoured to confirm this observation so far as the species under notice is concerned, but have not been able to do so. There seems to be always a spirally coiled thread encased in a transparent tube or sheath. The nearest approach to an axis bearing a screw is when the coils are thrown close together, as often happens. I have added a sketch (fig. 7) of a close portion of a coil, drawn from the ¼ in. objective with the camera lucida.
Female.—The only female specimen I have been able to obtain is a very small one (about 2 inch. in length) and much mutilated. The organs I have been able to observe are the long, narrow, nidamental glands, lying on the median line just above the gills, the oval flat and apparently stalked accessory glands immediately below them, and the ovary. The ovary in this specimen is very small and is somewhat pyramidal in shape, the apex lying at the upper end of the body. I am not sure that I have correctly observed the oviduct, but what I take to be the oviduct opens on the left side, having passed under the branchial heart.
(Note.—The fact that this specimen is the only female among ten that I have examined, and that the males were all fully ready for congress, would seem to show that sexual selection may have considerable scope among the members of this species.)