118 MIMICRY, AND OTHER PROTECTIVE 
ings as to make them specially visible. Mr. Darwin 
had put the case to me as a difficulty from another 
point of view, for he had arrived at the conclusion that 
brilliané colouration in the animal kingdom is mainly 
due to sexual selection, and this could not have acted 
in the case of sexless larvee. Applying here the analogy 
of other insects, I reasoned, that since some caterpillars 
were evidently protected by their imitative colouring, 
and others by their spiny or hairy bodies, the bright 
colours of the rest must also be in some way useful to 
them. I further thought that as some butterflies and 
moths were greedily eaten by birds while others were 
distasteful to them, and these latter were mostly of con- 
spicuous colours, so probably these brilliantly coloured 
caterpillars were distasteful, and therefore never eaten 
by birds. Distastefulness alone would however be of 
little service to caterpillars, because their soft and juicy 
bodies are so delicate, that if seized and afterwards re- 
jected by a bird they would almost certainly be killed. 
Some constant and easily perceived signal was therefore 
necessary to serve as a warning to birds never to touch 
these uneatable kinds, and a very gaudy and conspi- 
cuous colouring with the habit of fully exposing them- 
selves to view becomes such a signal, being in strong 
contrast with the green or brown tints and retiring 
habits of the eatable kinds. The subject was brought 
by me before the Entomological Society (see Proceed- 
ings, March 4th, 1867), in order that those members 
having opportunities for making observations might do 
so in the following summer ; and I also wrote a letter to 
