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Show 668 MR. J. GRAHAM KERR ON THE [June 1 8, of the coelom, having the characters already mentioned, and at the opening at the oral (ventral) end of the ovary this is inflected into its interior so as to line this likewise. The cavity of the ovary is thus merely an incompletely shut-off portion of the coelom. Traced into the interior ot the ovary, the epithelium about its opening assumes a columnar form and bears long cilia (cil.ep.). Along its roof the cells become shorter and eventually cubical. About two-thirds of the way from the mouth of the cavity the ovigerous region is reached, and this occupies the remainder of the roof and nearly the whole of the floor of the ovary. Tbe ovigerous region of the cavity is thickly beset with egg-follicles of various ages (ov.foll.). In the recesses between the bases of these the lining epithelium-a thin protoplasmic layer with scattered nuclei and indistinct division into cells-thickens up into syncytial masses of protoplasm containing large round nuclei, each with a large deeply staining nucleolus, around which the protoplasm tends to segregate off more or less distinctly. The primitive ovum develops within such a heap, the nucleus increasing in size and assuming more and more the character of a " germinal vesicle," and the protoplasm first becoming more distinctly aggregated round the nucleus and marked off from the surrounding protoplasm and then increasing rapidly in size. A s the ovum increases in size the substance of the ovarian wall grows up round it to form the follicle, while the syncytium accompanying the ovum apparently gives rise to the lining-cells of the follicle. The latter are pear-shaped structures borne on stalks, which are usually simple, but occasionally branch, thus showing a tendency towards the condition in Argonauta, where they are much branched and tree-like. Externally the follicle is covered by a very thin epithelium, which distally becomes continuous with the lining layer of " follicle-cells " - a layer of thick columnar cells immediately surrounding the egg. In the young follicle this layer runs concentrically with the outer surface of the epithelium, but as the egg increases in bulk an increase in the surface of this apparently nutritive organ becomes necessary and the follicle-epithelium grows inwards as a series of anastomosing folds. O n this account the older eggs when removed from the follicle show on their surface a network of deep fissures formed by the follicular epithelial ingrowths. In the oldest female specimen accessible, unfortunately too macerated to make out many details, the eggs had reached a large size, over 10 m m . in length, and their substance was already enormously yolk-laden, the protoplasm being practically restricted to a small cap on the end of the egg next the follicular opening. Imbedded in this was the large nucleus with densely staining nucleolus. The presence of a definite opening in at least the older follicles and the position of the egg-nucleus close to this, suggest the possibility of fertilization in Nautilus being internal; and the great size of the eggs and their yolk-laden character point to the segmentation being meroblastic as in other Cephalopoda. The wall of the ovary, as of other important organs, is loose and spongy, traversed by extensive blood-sinuses (b.s.). Prolongations |
