THE LEPIDOPTERA. 
91 
their growth really form a most important part of the phenomena 
of evolution, for some very necessary alterations in the internal 
structures progress especially during the last stage of quiet retire- 
ment which accompanies the final change of skin before the 
commencement of the chrysalis state. 
Although several broods of caterpillars are born in a year 
in such species as Anthocharis belia and Vanessa prorsa , yet 
CHRYSALIDES SLUNG AND SUSPENDED. 
the successive larvae present no distinctions in their external 
ornamentation, but the perfect insects which are metamorphosed 
from these similar larvae do differ very materially. Yet the 
butterflies of Vanessa Io , a species closely allied to Vanessa 
prorsa , are always the same, notwithstanding there are successive 
broods of them in the year. 
This variation in the colouring and ornamentation of the 
butterflies of successive broods is most interesting, especially 
when it is considered in relation to the opposite state of things 
so common in some species of moths, whose generations of 
caterpillars differ, the perfect insects remaining unaltered. The 
