Page:Natural History Review (1861).djvu/493

Rh developments of the passages connecting the genital with the renal chamber.

As the glandular appendages of the venæ cavæ are now generally acknowledged to be of a renal nature, the office of the chamber containing them is, apparently, to receive the urine as it la secreted, and then to expel it through the nipple-shaped orifices situated in the branchial chamber. And the genital, which we have seen communicates with the renal chamber, may be looked upon as an extension of the latter; the same membrane undoubtedly forming the walls of both chambers. In the renal chamber proper this membrane is in part specialized, forming the glandular appendages attached to the venæ cavæ, the blood channels themselves only supplying the vessels that permeate these organs. The effete, nitrogenous and more solid matters of the urine are probably eliminated by these glandular appendages, which take upon themselves the function of the urinary tubules of the kidneys of the higher animals; while the other great chamber, the genital, receives the fluid, perhaps little more than water, that may be supposed to flow from the arterial capillaries of the various organs placed within it. Assuming this to be the case, then this chamber will be related functionally to these capillaries as the capsule of the malphigian tuft is to the capillaries of the tuft itself. The fact appears to be, that the kidney in these, as in most other mollusks, is diffused, or not fully specialized; but nevertheless here, as in the higher animals, the more solid products of the urinary secretion are abstracted by the agency of secreting cells, and the fluids principally by the action of mere capillary blood-vessels.

This, then, is apparently the primary function of these so-called water chambers; but lymph may also be supposed to escape into them during the act of nutrition, and mingle with their fluid contents. This, however, is perhaps more strictly the case with regard to the genital chamber, in which the fluid is probably little else than lymph and pure water; the valvular nature of the orifices connecting this chamber with that containing the glandular appendages preventing the fluids of the latter passing into the former. The deleterious urinary matters are consequently always confined to the renal chamber proper.

Now we have seen that the cardiac appendages are always bathed by this fluid, both externally and internally, however the parts may be modified; that their lining membrane is raised into folds and wrinkles, which are clothed with minute papilla?, thus giving great increase of surface; that the papillæ are filled with granular cells, and are in connexion with a highly vascular parenchyma, and that the trunks of the vessels permeating this parenchyma, open into the branchial hearts. It is therefore evident, from the structure of these enigmatical organs, that they are well calculated for the selection and absorption of fluid matters. I would suggest, then, that we see in these cardiac appendages an apparatus for the return to the system of the extravasated lymph that may have escaped into the genital