920 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



circular fibres appears. This portion of the alimentary canal lies in a spacious recess in the 

 liver, and two lateral hepatic masses abut upon, but do not actually arch over it. In the 

 post-larval wrasse a similar relation of the canal and the liver is noted. The prominent 

 wrinkles of the gut in Anarrhichas disappear about the region of the pectoral fins, the 

 canal forming a rounded thick-walled tube with one or two triangular folds. After passing 

 the yolk-sac the canal is larger than in front, and transversely elongated in section, the 

 mesenterial band fixing it to the roof of the abdominal cavity, though it is free elsewhere. 

 Its contour is, however, broken superiorly by the wall of the large portal vessel. A com- 

 paratively smooth portion of the gut follows, but folds again make their appearance, in 

 the form of five or six prominent rugae in section. The mesentery dorsally is thickened, 

 and is almost divided into two portions by a constriction — an upper rounded band, and 

 a lower — which is thinned off superiorly. The ruga? now diminish, the mesentery disappears, 

 and the urinary vesicle takes its place, while the anus opens externally. Proceeding 

 backward, the epithelium of the gut is found to become finer and larger ; indeed, in section, 

 posteriorly, it resembles that so characteristic of the alimentary wall in the Annelida ; 

 then the folds reappear towards the rectum, and show a somewhat radial striation. 



The alimentary canal in the young salmon differs considerably from the foregoing in 

 the region just behind the branchiae, since it forms a lax tube in transverse section, with 

 thin walls greatly flattened from above downward. The wall increases in thickness in 

 the region of the pectoral fins, and the circular coat assumes larger dimensions, so that 

 the canal is less flattened. It is comparatively small for the size of the fish, the lumen 

 being really smaller than that of the aorta. Towards the posterior part of the pectorals 

 the gut is even less than in front of them. The epithelial (mucous) layer then begins 

 to increase, and a folded condition of the gut causes two layers to appear in transverse 

 section, a smaller superior and a larger inferior. In front of the liver the small calibre of 

 the epithelial coat is in contrast with the thick circular (glandular) layer outside. 

 In the hepatic region the lumen of the gut greatly enlarges, though it is still proportionally 

 less than in the wolf-fish. Behind the liver it slightly diminishes in diameter, and again 

 somewhat enlarges, before assuming the rounded condition characteristic of the rectum, 

 the calibre of which is also smaller. The folds of the gut are much less prominent than 

 in the wolf-fish ; and the inner surface of the large cylindrical cellular layer of the rectum 

 is almost smooth. Some of these features, however, may partly be due to the state of the 

 preparations. In the newly-hatched and living salmon, again, the alimentary canal appears 

 between the yolk-sac and the anus as a greenish band. About the tenth day distinct 

 transverse markings are observed in the tract, two especially conspicuous above the origin 

 of the ventral fin. Between the fourth and fifth weeks, the functional activity of the 

 alimentary canal is considerable, and numerous faecal masses occur in the rectum. The 

 teeth are now evident in both upper and lower jaws. A little later food of various kinds 

 is found in the stomach and intestine. The pyloric caeca on the nineteenth day form mere 

 conical elevations on the duodenum, and have the aspect of short papillae of a cellulo- 

 granular nature. It is remarkable that the pancreas (assuming the caeca to represent it) 



