MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 203 



outer attached edge of the ovarium membrane forming a channel with a very narrow 

 roof of dorsal peritoneum. The two oviducts unite near the outlet. This alewife has a 

 ventral mesentery of about the same relative extent as in the salmonids. 



The hyodons are stated (Jordan and Evermann, 1896, p. 412) to have no oviducts, 

 the eggs falling into the abdominal cavity before extrusion. An example of Hyodon 

 tergisus in breeding condition showed that the ovaries are completely inclosed in mem- 

 brane which, continuing from the mesovarium junction with the ovary, passes down 

 its inner surfaces and up over the outer surface and upper edge, then downward again 

 on the inner surface to the mesovarial attachment. The fusion of the outer edge of 

 the ovarian covering with the mesovarium at its junction with the ovary appears to be 

 complete as far back as the common opening in the dorsal mesentery. In this speci- 

 men the remainder of its backward extent seems to be still attached by fascialike, adhe- 

 sive membrane similar to the adhesions of the viscera in general to the abdominal wall 

 and to each other. At the termination of the mesentery posteriorly in the common 

 opening an interovarian channel is formed by the continuation of the ovarian mem- 

 branes. The membranes of the inner surface of each ovary fuse along the median longi- 

 tudinal line of the upper surface of the intestine, forming the floor of a common ovi- 

 ducal channel, the outer sides of which are formed by the ovarian membranes of each 

 ovary, beginning on the inner surface as a projecting fold. At this point the intestine 

 and canal somewhat abruptly turn downward to the outlet. Another mesovariumlike 

 membrane on each side begins forward, originating close to the mesovarium, and is 

 attached to the upper surface of the ovary. It appears to continue backward beyond 

 where the dorsal attachment of the true mesovarium ends and, b)' adhesion to the outer 

 edge of the oviducal canal on each side, respectively, forms a closed oviduct. Except- 

 ing in this secondary membrane, this oviducal structure is very similar to that which 

 has been described in connection with the Salmonidae. 



Since the intestine, with the superimposed oviducal canal, for the most of its extent 

 is ddrsally situated, it is quite evident that any ova falling into the abdominal cavity 

 can not be extruded. 



RELATION OF THE ANATOMICAL FACTS TO FISH-CULTURAL PRACTICES. 



Boulenger (1904, p. 568) says of the Salmonidae: 



The large size of the eggs, their lack of adhesiveness, and the fact that the ova fall into the abdom- 

 inal cavity, out of which they may be easily squeezed, renders artificial impregnation partictilarly easy 

 and the species of Salmo have always occupied the first place in the annals of fish culture. 



The error of this statement has been shown in the foregoing pages. It has been 

 seen that the mature ovary is inclosed in a delicate membrane, which is a continuation 

 of the peritoneal fold called the mesovarium. From the posterior end of each ovary an 

 open membranous trough extends inward and backward to the median line of the upper 

 surface of the intestine at the posterior termination of the dorsal mesentery, whence, by 

 a fusion with each other mesially, a single oviducal trough, open above, which conveys 

 the ova to the genital pore, is formed on the upper surface of the intestine. 



Inasmuch as the ova do not naturally fall into the abdominal cavity and can not be 

 extruded if they are displaced into it, it follows that their adventitious presence there 

 can not be of advantage to the fish. Fish-cultural methods afford several means of 



