OCR Text |
Show 1883.] PROF. HUXLEY ON THE OVIDUCTS OF OSMERUS. 133 " In the Smelts (Stinten), however, there passes from each ovary a band, one edge of which is attached to the dorsal, tbe other to the abdominal wall, so that, in each lateral half of the abdominal cavity, there is a chamber which receives the eggs when they are detached from the ovary. The two chambers ultimately unite above the anus; and, in fact, close in front of the place where, in other fishes, the oviduct is situated. " Thus the Smelts appear to present a remarkable transition to that structure of the oviduct which alone is met with in the other classes of the Vertebrata. Instead of tbe oviduct having, as in these, the character of an independent tube, in the Smelts only one half ot it is found, and yet this has united in such a way with the wall of the abdominal cavity that a part of this wall takes the place of the other half of the oviduct." And, further, at page 159 :- " That a proper oviduct is absent in the Salmon tribe has already been stated, and also that they possess an analogue of that structure. This consists of a flat, narrow band, which commonly arises at the upper and posterior end of the plate-like ovary, gradually diminishes in width backwards, and finally becomes lost towards the end of the abdominal cavity. In the Salmon proper it disappears upon the air-bladder, opposite the commencement of the last fifth of the abdominal cavity, in the freshwater Trout on the sides of the intestine not far from the anus, in the Coregoni (Maranen) on the intestine close to its end. "The transition from this band-like membranous process of the ovaries of the higher Salmonoids to the oviduct of most fishes is remarkably exemplified in the Smelts. In these, in fact, a delicate membranous process, a mere fold of the peritoneum, proceeds from the end of each ovary, the upper edge of which is attached to the renal organ, the lower to tbe wall of the abdomen. In this way a cavity lies behind each ovary, bounded externally by tbe wall of the abdomen, and internally by this band. When the eggs are detached they fall into these cavities, which become narrower behind, and leave the body by a common aperture which lies behind the anus. The end of the intestine lies between the two cavities ; and since the left ovary lies far from the posterior end of the abdominal cavity, the singular oviduct which has just been described has, on tbe left side, a considerable length ; the right oviduct, however, is very short, the right ovary being situated so far back." Rathke finally observes (p. 160) that he does not consider the condition of the ovaries in the Salmonoids, Eels, and Lamprevs to represent the lowest condition of these parts in fishes, but rather to result from the subdivision of the reproductive organ into two separate parts-the one productive, and the other educative. I am not aware that, since Rathke wrote, any one has paid attention to the remarkable arrangement which he describes; and though I have often intended to look into the matter myself, it is only lately that I have carried my design into effect. |