INSECT SIPPERS AND GNA WERS. 235 
special mouth and stomach (see p. 78), while a 
second and differently shaped form, with a mouth 
and stomach and feet of its own, is growing up 
inside ; yet both these beings are part of one single 
creature, and when the form within is ready to get 
its own living, it swallows its earlier self and goes its 
way. So too the headless mollusca, such as the oyster 
and cockle, swim about in their young life and have 
eyes which they lose when they settle down, while the 
crab undergoes such complete changes (see Fig. 59, 
p. 167) that no one would recognise parent and child 
if they saw them together. 
We learn then that it is not the exception, but 
in many cases the rule for a creature to take on 
different forms at different times of its life ; and the 
chief novelty in the metamorphosis of insects turns 
out to be that they have learnt to do one thing at a 
time, and after passing their early life in incessant 
feeding and storing up of material for a more perfect 
body, they retire from the world to spend all their 
energy in building up those new and beautiful bodies 
which we admire so much in the lovely painted 
butterfly or the gorgeous metallic-winged beetle. 
Nor shall we wonder that this quiet is necessary 
when we understand the marvellous change which 
takes place in them. The cockroach and the cricket 
only gain wings by their last change of skin, and 
though the May-fly alters its apparatus for breathing 
so as to be able to live in the air, still the greater 
part of its body remains the same. But the cater- 
pillar and the grub have actually to remodel every 
part of their bodies in order to become the butterfly 
or the beetle, and we can scarcely say that any 
