234 LIFE AND HER CHILDREN. 
burrowed as maggots or grubs in decaying matter, or 
in the trunks of trees, or in the fruits and flowers of 
plants ; or still less that each active hopping flea 
once rolled about helplessly as a little hairy grub 
and span a tiny silk cocoon, in which its present 
body was formed ? 
To those who have only paid attention to the 
higher animals, such as birds, fishes, and quadrupeds, 
which, when they are born have already assumed a 
fairly settled form, this springing up of one being 
out of the husk of another apparently quite unlike it, 
seems strange and unnatural ; and in olden times all 
kinds of fanciful ideas were connected with the 
metamorphosis of insects. But if we begin, as we 
have now done, by Life's simplest children, and see 
how in each successive group the necessity for 
making the best of everything causes many creatures 
to alter their form and habits at different periods of 
their lives, then these curious changes in insects have 
a real meaning, and we can set to work patiently in 
the hope of discovering what advantage they are to 
the creature which undergoes them. 
Thus, for example, we have already found the 
sponge beginning as a swimming animal (see p. 38), 
and then drawing in its lashes and settling down to 
build a solid skeleton clothed with a colony of cells ; 
while the lasso-throwers begin by swimming, go on 
as stationary, branching and budding animals, and 
end by throwing off egg-bearing jelly-bells quite as 
unlike the animal tree as a butterfly is unlike a 
caterpillar. In the star-fish and sea-urchins the 
transformation scene is still more curious, for the 
jelly-animal is swimming about and feeding with its 
