es possess at
least some winged members. On the rose-bush, you can generally pick off
a few such larger winged forms, side by side with the wee green wingless
insects. But creatures which have taken to passing most of their life
upon a single spot on a single plant hardly need the luxury of wings;
and so, in nine cases out of ten, natural selection has dispensed with
those needless encumbrances. Even the legs are comparatively little
wanted by our modern aphides, which only require them to walk away in a
stately sleepy manner when rudely disturbed by man, lady-birds, or other
enemies; and indeed the legs are now very weak and feeble, and incapable
of walking for more than a short distance at a time under exceptional
provocation. The eyes remain, it is true; but only the big ones: the
little ocelli at the top of the head, found amongst so many of their
allies, are quite wanting in all the aphides. In short, the plant-lice
have degenerated into mere mouths and sacks for sucking and storing food
from the tissues of plants, provided with large honey-tubes for getting
rid of the waste sugar.

Now, the greater the amount of food any animal gets, and the less the
amount of expenditure it performs in muscular action, the greater will
be the surplus it has left over for the purposes of reproduction. Eggs
or young, in fact, represent the amount thus left over after all the
wants of the body have been provided for. But in the rose-aphis the
wants of the body, when once the insect has reached its full growth, are
absolutely nothing; and it therefore then begins to bud out new
generations in rapid succession as fast as ever it can produce them.
This is strictly analogous to what we see every day taking place in all
the plants around us. New leaves are produced one after another, as fast
as material can be supplied for their nutrition, and each of these new
leaves is known to be a separate individual, just as much as the
individual aphis. At last, however, a time comes when the reproductive
power of the plant begins to fail, and then it produces flowers, that is
to say stamens (male) and pistils (female), whose union results in
fertilisation and the subsequent outgrowth of fruit and seeds. Thus a
year's cycle of the plant-lice exactly answers to the life-history of an
ordinary annual. The eggs correspond to the seeds; the various
generations of aphides budding out from one another by parthenogenesis
correspond to the leaves budded ou