Life-history of Salmon. 117 



licrbivorons animals, for all ^n!C!ri parts of plant-; contain also 

 a certain amount of }-ello\v ])igment " (p. 163). 



The difficulty is met by the conclusion " that the presence 

 of pigment-containing- fat in cattle, in caterpillars, and in the 

 Fulmon is due in each case to the habit of ingesting coloured 

 fatty food in an amount which is in excess of the immediate 

 )f quirements, the consequence being that fat coloured with 

 the |)ignient in a more or less modified condition is deposited 

 in certain of the tissues. While the pigment so dejjosited 

 is of no importance in cattle, in caterpillars it is important in 

 producing the external coloration and in the salmon in 

 colouring the ova. In the male salmon the j)igment is 

 probably eliniinated as the fat is used up. The question is 

 of some interest, because if the suggestion here made be 

 correct, it shows that a characteristic pigmentation may be 

 acquired, as it were, incidentally in the life-history of the 

 individual under circumstances which render the question as 

 to the inheritance of acquired character absolutely unim- 

 portant" * (p. 1(?4). 



In the general summary of results Dr. Noel Paton comes 

 to the rather surprising conclusion that '' it wouKl thus seem 

 to be the state of nutrition which is the factor determining 

 migration towards the river ; that when the salmon has accii- 

 mxdated the necessary supply of material it tends to return to 

 its original habitat " (p. 170). This conclusion is based on 

 tlie fact that the Salmonidas are originally freshwater fish, 

 the majority of which spend their whole life in fresh water. 

 Others, like the Salmon, have a|)j)arently acquired the habit 

 of quitting the fresh water in search of food, having accumu- 

 lated a store of which in the body^ the fish returns to its 

 native element, and there performs its reproductive act. 



" That tiie migration of the fish is not governed by the 

 growth of the genitalia and by the nisus generativus f is," the 

 author tliinl;?, " shown by the fact that salmon are ascending 

 rivers throughout the whole year with their genitalia in all 



• I do not think it likely thut either Miss Newbigin's conclusions as to 

 the origin of the red pigment or Dr. Noel Paton's (see below) as to the 

 cause of the return of the salmon to fresh water will be accepted without 

 further discussion. Neither question, however, directly concerns the 

 subject of this paper, and no good object would be obtained by devoting 

 space to their treatment. 



t Renewed investigations by Dr. Noel Paton and Misg Newbi;rin (Proc. 

 R. Soc. Edinburgh, Sess. 1899-1900) lead them to strengthened opinions 

 that " the Salmon goes to the sea to feed and returns to the river when it 

 has accumulated its full store of nourishment irrespective of the condition 

 of the reproductive oryans. The factor determining migration from oca to 

 river it< ?iot the ni-'us generativus, but the ftate >f nutrition." 



