MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 189 



One authority (Wiedersheim, Parker, 1897) states that the male and female gonads 

 of teleosts closely correspond with one another as regards position and the arrangement 

 of their ducts. Dorsal and ventral folds of the peritoneum are developed in connection 

 with the elongated ovary, and these in most cases meet along its outer side, so as to 

 inclose a portion of the coelome, and thus convert the ovary into a hollow sac, blind 

 anteriorly, on the inner folded walls of which the ova arise; this sac is continued back- 

 ward to form the oviduct, which is generally short and fuses with its fellow to form a 

 tube or "ovipositor"; or the ducts may communicate with the urogenital sinus. 



The same authority describes the development of the ovary as originating in at 

 first undifferentiated cells of coelomic or peritoneal epithelium on the dorsal side of 

 the body cavity at either side of the mesentery in which the adjacent mesoblastic stroma 

 penetrates. Into the stroma of an ovary thus formed, the cells of germinal epithelium 

 grow in the form of clustered masses; some of which cells increase in size more than 

 others, giving rise to ova, while the smaller cells form investment of follicle around each 

 and serve as nutritive material. 



From the foregoing it is understood that the ovaries of most teleosts are derived 

 from folds of the peritoneum, usually one on each side of the body cavity, and, as a 

 rule, are closed sacs consisting of an outer enveloping membrane and inner laminae of 

 ovigerous stroma. Each egg is inclosed in a follicle from which, as it ripens, it breaks 

 out into the inner or central cavity of the ovary and makes its exit from the fish by the 

 way of a tube, or oviduct, of the same membrane and the genital pore. 



Some exceptions to this arrangement have been noted. Something over 90 years 

 ago, Rathke (1824) described the ovarian membranes of certain salmonoid fishes, and 

 nearly 60 years later Huxley (1883) reviewed Rathke's work, from which he quotes as 

 follows : 



In certain fishes the oviducts have entirely disappeared; this is the case in the eel, the sturgeon, 

 Cobiiis tcEtiia, and in the lamprey. In others, however, such as the higher kinds of salmonoids, there 

 extends back behind each ovary a narrow band which may, be regarded as the remains of an oviduct. In 

 all these fishes, therefore, the central abdominal cavity must take the place of an oviduct, as it receives 

 the eggs when they are detached, and allows them to make their exit by a single opening at its posterior 

 extremity. 



Still quoting from Rathke, Huxley continued to the effect that, while a proper 

 oviduct is absent from the Salmonidae, there is an analogue of that structure, consisting 

 of a flat, narrow band, commonly arising at the upper and posterior end of a platelike 

 ovary, gradually diminishing in width backward, and fmally becoming lost toward the 

 end of the abdominal cavity. It was stated that in the salmon proper it disappears 

 upon the air bladder opposite the commencement of the last fifth of the abdominal 

 cavity; in the fresh- water trout on the sides of the intestine not far from the anus; in 

 the whitefishes (Coregoni) on the intestine close to its end. 



In describing the ovary of the European smelt Osmerus eperlanus, which was at that 

 time regarded as a member of the salmon family, Huxley stated that in all essentials of 

 the structure of the ovigerous portion or body it agreed with that of the other Salmonidae. 

 It was said to have the form of a half-oval plate, with the curved edge ventral and the 

 straight edge dorsal. To the latter a narrow mesovarial fold of the peritoneum was 

 said to extend "from that part of the dorsal wall of the abdominal cavity which corre- 

 sponds with the ventral surface of the air bladder" and the line of attachment to be 

 75412°— 22 13 



