same period, and can be perpetuated and increased by selection without
modifying other parts of the organisation. Thus, variations in the
caterpillar or the cocoon of the silkworm, in the eggs of poultry, and
in the seeds or young shoots of many culinary vegetables, have been
accumulated till those parts have become greatly modified and, for man's
purposes, improved. Owing to this fact it is easy for organisms to
become so modified as to avoid dangers that occur at any one period of
life. Thus it is that so many seeds have become adapted to various modes
of dissemination or protection. Some are winged, or have down or hairs
attached to them, so as to enable them to be carried long distances in
the air; others have curious hooks and prickles, which cause them to be
attached firmly to the fur of mammals or the feathers of birds; while
others are buried within sweet or juicy and brightly coloured fruits,
which are seen and devoured by birds, the hard smooth seeds passing
through their bodies in a fit state for germination. In the struggle for
existence it must benefit a plant to have increased means of dispersing
its seeds, and of thus having young plants produced in a greater variety
of soils, aspects, and surroundings, with a greater chance of some of
them escaping their numerous enemies and arriving at maturity. The
various differences referred to would, therefore, be brought about by
variation and survival of the fittest, just as surely as the length and
quality of cotton on the seed of the cotton-plant have been increased
by man's selection.

The larvae of insects have thus been wonderfully modified in order to
escape the numerous enemies to whose attacks they are exposed at this
period of their existence. Their colours and markings have become
marvellously adapted to conceal them among the foliage of the plant they
live upon, and this colour often changes completely after the last
moult, when the creature has to descend to the ground for its change to
the pupa state, during which period a brown instead of a green colour is
protective. Others have acquired curious attitudes and large ocelli,
which cause them to resemble the head of some reptile, or they have
curious horns or coloured ejectile processes which frighten away
enemies; while a great number have acquired secretions which render them
offensive to the taste of their enemies, and these are always adorned
with very conspicuous markings or brilliant colours, wh