1 88 BULLETIN OF THE BUREAU OP FISHERIES. 



as in the lamprey (Petromyzon), to a few filaments accompanying the intestinal blood 

 vessels. 



The dorsal mesentery of Salmonid.^. — In adult Salmonidae the supporting 

 membrane of the alimentary tract diverges from near the longitudinal median line of 

 the peritoneal covering of the air bladder and is attached to the upper surface of the 

 canal as follows: From the diaphragm (fig i k) and along the mesial line of the air 

 bladder (fig. i ■z;), a fold (fig. i s) is sent out to the upper surface of the stomach on 

 which it ends near the posterior bend or sometimes extends to the spleen (fig. i m). 

 The pyloric arm has no supporting membrane, but is connected to the cardiac arm of 

 the stomach by filamentous bands, though sometimes anteriorly there may be a trace 

 of membrane. Again, beginning near the diaphragm is another fold (fig. i /), which, 

 attached to the backward prolongation of the intestine, extends nearly to the vent in 

 the female and quite to the vent in the male. 



The ventral mesentery. — Concerning fishes in general. Bridge writes that the 

 ventral mesentery is rarely present and, if present, is never complete. In Lepidosteus 

 a ventral mesentery is said to be present in connection with that part of the intestine 

 which contains the spiral valve. In Protopterus, and also in Neoceratodus, there is a 

 well-developed ventral mesentery in relation with the greater part of the length of the 

 intestine, although in the former Dipnoid its continuity is interrupted by one or two 

 vacuities, and in the latter the mesentery is incomplete posteriorly. A ventral mes- 

 entery is also present in the intestinal region of some of the Muraenidae among teleosts, 

 but no mention is made of it in Salmonidae. 



I have examined four species of Oncorhyncus {0. kisuich, 0. gorbuscha, 0. 

 tschawytscha, and 0. nerka) ; several species of Salmo (S. salar, S. sebago, S. trutta, 

 S. gairdnerii, and S. shasta) ; and several Salvelinus {S. stagnalis, S. aureolus, S. oquassa, 

 S. marstoni, S. malma, S. kundsha, and S. fontinalis), all of which possess a certain 

 extent of ventral mesentery (fig, i u). Its anterior ventral insertion is a little be- 

 hind the base of the ventral fins, and the corresponding intestinal insertion somewhat 

 in advance of the ventral insertion, thus presenting a vertical concave edge toward 

 the front. This mesentery in its ventral and intestinal attachments extends to the 

 posterior end of the abdominal cavity. According to Felix (1906) the embryo salmon 

 has a complete ventral mesentery. 



By these vertical dorsal and ventral mesenteries and the intestine to which both 

 are attached, about one-third of the abdominal cavity is posteriorly divided into two 

 lateral longitudinal chambers, with a posterior communicating aperture of varying 

 length, but always short, in the dorsal mesentery above the intestine of the female. 



STRUCTURE AND DEVELOPMENT OF GENITAL ORGANS OF FISHES IN GENERAL. 



The suspensory portion of the ovarian membrane is known as the mesovarium, 

 or mesoarium, and that of the spermary as the mesorchium. Morphologists state that 

 the gonads of the majority of teleosts are completely enveloped by the peritoneal mem- 

 brane and that the ova and sperm of oviparous forms are conveyed to the exterior of 

 the body cavity by closed canals or tubes composed of the same enveloping membrane 

 extending from the gonad to the genital pore (fig. 2 h). The previous state of 

 knowledge regarding especially the ovarian membranes of Salmonidae is well indicated 

 by the following review of the opinions or statements of principal writers. 



