V NATURAL SELECTION 113 



of cotton on the seed of the cotton-plant have been increased 

 by man's selection. 



The larvse 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 j^l^nt 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 bro^ATi instead of a 

 green coloiu* 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 

 •\vdth 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 gTeat 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 



