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 
