V 
NATURAL SELECTION 
113 
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, which 
serve as a sign of inedibility and prevent their being needlessly 
attacked. This, however, is a portion of the very large sub¬ 
ject of organic colour and marking, which will be fully dis¬ 
cussed and illustrated in a separate chapter. 
In this way every possible modification of an animal or 
plant, whether in colour, form, structure, or habits, which 
would be serviceable to it or to its progeny at any period of 
its existence, may be readily brought about. There are some 
curious organs which are used only once in a creature’s life, 
but which are yet essential to its existence, and thus have 
very much the appearance of design by an intelligent designer. 
Such are, the great jaws possessed by some insects, used ex¬ 
clusively for opening the cocoon, and the hard tip to the beak 
of unhatched birds used for breaking the eggshell. The 
increase in thickness or hardness of the cocoons or the eggs 
being useful for protection against enemies or to avoid 
accidents, it is probable that the change has been very 
gradual, because it would be constantly checked by the 
necessity for a corresponding change in the young insects or 
birds enabling them to overcome the additional obstacle of a 
tougher cocoon or a harder eggshell. As we have seen, 
however, that every part of the organism appears to be 
varying independently, at the same time, though to different 
I 
