20 



Investigations on the Life- History 

 (a) Fish at the Mouth of the River ; 



or, in Percentage of Fish Taken. 



Distended. 



Empty. 



(fe) 7''is/i in Upper Waters. 

 In all the gall bladders were collapsed. 



(c) Kelts. 



In most of these the gall bladders were distended. 



I examined several gall bladders microscopically, and they all, whether 

 distended or empty, whether from fish at the mouth of the river, in the 

 upper waters, or from kelts, showed a desquamative catarrh of exactly 

 the same kind as that described in the stomach, intestine, etc. In some 

 the epithelium had entirely disappeared, while in others part of it could 

 be seen in a degenerated state, either lying detached in the lumen of the 

 bladder, as was more usual, or attached in fragments to the wall. There 

 is no stratum compactum in the gall bladder ; the connective tissue was 

 in a state of more or less evident hyaline degeneration. 



CONCLUSIONS. 



We may take it for granted that at some period of its existence the 

 salmon's alimentary tract has the same normal structure as that of the 

 trout, and it is evident that its sojourn in the sea is the time of normal 

 digestive activity. Probably for some time before the fish enter the 

 river, and certainly while they are lying at the mouth of it, the catarrhal 

 change begins, and begins clearly in the intestine and pyloric append- 

 ages ; the stomach is at that time unaffected. By the time the fish have 

 reached the upper waters the stomach has been attacked, and the 

 whole digestive tract is in a state of catarrh. After spawning is over, 

 the stomach is the first part to recover, and in the kelts it is again histo- 

 logically normal, while the intestine and pyloric appendages probably 

 recover when the fish have returned to the sea. 



