XV 
THE RELATION OF FACTS TO THEORIES 
3*7 
The author then proceeds to discuss various cases, 
of which the first is an example rather of protective 
coloration than of mimicry proper. It is the case of 
the colour-change of the caterpillar in the Sphingides 
from green to brown just before pupation. The 
caterpillar feeds among green leaves and is then 
green, but it forms a chrysalis in earth, and the 
brown colour has been held to be of protective 
importance during the period when the caterpillar is 
in search of a retreat. Piepers, however, observes 
that the period which elapses between the cessation 
of feeding and the formation of the chrysalis is 
exceedingly short, in some cases not more than some 
minutes ; that the brown is constant, while the tint of 
the earth varies and is often quite different ; and that 
as the caterpillar is necessarily moving all the time, 
a protective colour can hardly be of much avail. 
Finally, the colour-change is exceedingly common in 
the larvae of Lepidoptera at this stage, and is probably 
due to a discoloration resulting from the drying up 
of the skin preparatory to its being shed. It occurs 
also in Sphinx larvae which are brown to begin with 
and not green, though here the change is so slight as 
to be little noticed. 
The next case taken up is that difficult one of 
the occurrence of several different forms among the 
females of certain Papilioms of India and the Malay, 
which was discovered and discussed by Mr. Wallace 
(; Trans. Linn. Soc. xxv. ; see also Contributions to the 
Theory of Natural Selection , London, 1871). The case 
is a somewhat difficult one, in part because the names 
used involve in themselves an interpretation of the 
facts. So far as it is possible for one who is not an 
