164 Investigations on the Life- History 



If we apply this explanation to the salmon, we have of course to face 

 the possibility that both the red and yellow pigment are ingested in 

 this way with the food. On the whole, this seems to me improbable, 

 and I am inclined to believe that it is only the yellow pigment which is 

 so obtained, but that owing to the conditions to which it is exposed in 

 the muscle, it becomes in part converted into the red, which then gives 

 rise to the colour of muscle and ova. 



It is interesting to observe that smolt which was kept at Howietoun 

 for three years developed ripe ova. These had the characteristic red 

 colour. (Day's British and Irish Salmonidse, p. 102). 



I am thus of opinion that the presence of pigment-containing fat in 

 cattle, in caterpillars, and in the salmon, is due in each case to the habit 

 of ingesting coloured fatty food in an amount which is in excess of the 

 immediate requirements, the consequence being that fat coloured with 

 the pigment in a more or less modified condition is deposited in certain 

 of the tissues. While the pigment so deposited 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 pig- 

 ment is probably eliminated 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 inciden- 

 tally in the course of the life history of the individual, under circum- 

 stances which render the question as to the inheritance of acquired 

 characters absolutely unimportant. 



