of the Salmon in Fresh Water. 



169 



III SUMMAEY OF EESULTS. 



17. GENERAL SUMMARY. 



BY D. NOEL PATON, M.D., F.R.C.P. ED. 



A. FACTORS DETERMINING MIGRATION. 



It has been generally assumed that the passage of the salmon from 

 the sea to the river is due to the nlsus generativus. In considering the 

 question it must be remembered that the Salmonidae are originally fresh- 

 water fish, and that the majority of the family spend their whole life in 

 fresh water. Salmo Salar and other allied species have apparently 

 acquired the habit of quitting their fresh- water home for the sea in 

 search of food, just as the frog leaves the water for the same purpose. 

 When, on the rich marine feeding grounds, as great a store of nourish- 

 ment as the body can carry has been accumulated, the fish returns to its 

 native element, and there pefonns its reproductive act. 



That the immigration of the fish is not governed by the growth of 

 genital ia and by the nisus generativus is shown by the fact that salmon 

 are ascending the rivers throughout the whole year with their genitalia 

 in all stages of development (p. 64). 



In fish leaving the sea the ovaries vary from 121 to 1439 grms. per 

 fish of standard length, but the accumulation of solids in their 

 muscles and ovaries together is about the same. 



Solids in Musde and Ovaries of Estuary Fish. 



* Or including all fish dealt with on p. 83: 

 Muscle, - - 1990 



