VII THE COLOURS OF THE LEPIDOPTERA 145 



may mean in the physiology of the individual. 

 Perhaps the following may not be thought to 

 transgress the bounds of legitimate speculation. It 

 is well known that the fats of different animals 

 are different both in their physical and chemical 

 characters. Now it has been found by experiment 

 that if an animal A be fed to excess with the fat 

 of another animal B, and the body of A be subjected 

 to subsequent examination, then the fat deposited in 

 it will not exhibit the normal characters of the fat 

 peculiar to the animal, but will partake more or less 

 of the characters of the fat of the food. In other 

 words, an animal is unable to impress its own 

 individuality on the fat of its food, if this be ingested 

 in excessively large quantity. Now we have seen 

 that in all probability the derived pigments consist, 

 at least in great part, of lipochromes, and we know 

 that in most cases the lipochromes tend to occur in 

 association with fats ; in chlorophyll the presence of 

 fat has indeed been directly affirmed. Is it not 

 possible that in the caterpillar — a notably voracious 

 feeder — a process occurs quite similar to that described 

 above for mammals ? That is, may not caterpillars, 

 which have a practically unlimited food-supply, be 

 unable to completely assimilate all the fat ingested, 

 but yet have the power of storing up in their tissues 

 this extra fat, and with it the pigment with which it 

 is associated in the food ? The process would thus 

 be very similar to that which occurs in the salmon, 

 where, as we have seen, both fat and pigment are 

 transferred from the muscles to the ovaries during 

 the period of fasting. If the assertion that in the 

 salmon the pigment is derived from the food is correct, 



L 



