The laminated glands doubtless serve to pro vide an exterior covering to the ova, and con nect them together, thus performing the func tion of the accessory external glands in the preceding tribe. The oviducts ascend behind the lateral hearts and venous cavities, and open on each side of the mediastinal septum of the branchial cavity opposite the middle of the gills (5, 5).
A glandular body surrounds each oviduct in Eledone, but is situated nearer the lower end of the tubes, and is of a darker colour than in Octopus.
In Argonauta the oviducts are continued by a short common passage from the ovary, and form several convolutions before they ascend to their termination, which is the same as in Oc topus ; they differ, however, from both the preceding genera in having no glandular lami nated bodies developed upon them : the minute ova of this genus are, therefore, connected together by the secretion of the lining mem brane of the long and tortuous oviducts.
In correspondence with the striking differences which the female organs present in the Cephalo podous class, it is found thafalmost every genus has its own peculiar form and arrangement of ova after their exclusion. Of these, therefore, we proceed to give a short description of the principal varieties.
The ova of the Argonaut are invariably found occupying a greater or less proportion of the bottom of the shell ; they are of an oval form, about half a line in length before the develop ment of the embryo has commenced, and are connected together in clusters by long filamen tary processes.
In the figure subjoined, (fig. 240), A repre sents the ova of the natural size, 13 a group of ova at an early stage of embryonic develop ment, magnified, C a single ovum, still more highly magnified, showing the embryo a, the rudimental feet b, and what would be regarded as the vitellus c, in the ovum of any of the naked Cephalopods, but which the continuator of Poli states to be the germ of the shell. With respect to the Poulp (Octopus) Aristotle states that the animals of this genus copulate in winter and bring forth in spring : that the female oviposits in a shell or some secure cavity; that the ova adhere in clusters, like the tendrils of the wild vine or the fruit of the white poplar, to the internal parietes of the cavity; that the young Poulps are hatched on the fifteenth day, and are then seen creeping about in prodigious numbers.* The ova of the Calamary (fig. 241) are in closed in cylindrical gelatinous sheaths, mea suring from three to four inches in length, and about a quarter of an inch in diameter at the thickest part, narrowing to an obtuse point at one end, and attached at the opposite extremity by a filamentary process, varying from half an inch to an inch in length, to some foreign body, as floating wood, &c.; each sheath or nidamen tum contains from thirty to forty ova, of a spherical figure, about a line and a half in diameter when newly excluded. As the num ber of cylinders attached to one body some times exceed two hundred, the prolific nature of the species may be easily conceived.
Fig. 242 shows the first appearance of the head and eyes a, at the stage prior to the development of the arms and funnel ; b is the elongated body, c the yolk-bag. Fig. 243 is another ovum at a more advanced stage of development : the pigmentum is now deposited both in the rete mucosum and in the eye ; the arms are just beginning to shoot from the ante rior circumference of the head ; and the little funnel may be observed rising above the ventral margin of the mantle.
The ova of the Sepioteuthis are also spherical and enveloped in cylindrical sheaths, but these are much shorter than in the Loligo, and contain much fewer ova, making an approach in this respect, as in the general organization, to the Sepiw, in which each ovum has its own nida mentum.
The eggs of the Cuttle-fish (fig. 244) are of an oval form, attenuated at the extremities, enveloped in a flexible horny covering, of a blackish colour, which is prolonged into a pe dicle at one extremity, and twisted round some foreign body. The length of ovum from the point of its attachment is generally an inch, and as a number of these ova are always found attached close together, and sometimes to one another, they resemble in this state a bunch of grapes, as the name sea-grapes,' coin monly given to them by the fishermen, implies.
In the development of the Cephalopod the most interesting circumstance, and one which had not escaped the notice of Aristotle,* is the point of attachment of the yolk-bag (c,fig. 245), which is suspended from the head of the embryo, its pe dicle being surrounded by the cephalicarms,and passing down anterior to the mouth to communicate with the pharynx. The yolk is a trans parent gelatinous fluid of a spherical form.
In the embryo of the Cuttle-fish all the organs, the exercise of' which is essential to its future welfare, are adequately developed before its exclusion. The gills are very distinct, and the respiratory actions are vigorously performed by the alternate dilatation and contraction of the mantle and a corresponding elevation and falling of the funnel (d), by which the little streams are expired. The ink-bag has already provided a store of secretion sufficient to blacken a considerable extent of water, and baffle any enemy which may be ready to remove the little Cephalopod from the world into which it is about to enter. The pigment of the rete mucosum is developed in several large spots, as in the Calamary (fig. 243).
Five concentric layers of the dorsal shell at least are deposited ; these are, however, horny, white, and transparent, except at the narrow and thick end; and the innermost layers are marked with irregular opake spots. The lateral fins are broad, and the ventral arms are furnished with a fin-like expansion, so that the young animal is enabled to execute movements either retrograde or progressive ; and the eyes are well developed and proportionally large to direct its evolutions.