Introduction. 3 



is for any two individuals to be subjected to exactly the same 

 conditions of life and habit. But for the proofs of variability we 

 have not to rely upon theoretical reasoning. No one can study, 

 even superficially, any class or species without daily experiencing 

 the conviction that no two individuals are alike, and that variation 

 takes place in almost every conceivable direction. 



Granted then the existence of the struggle for existence and 

 the variability of individuals, and granting also that if any varia- 

 tion gives its possessor a firmer hold upon life, it follows as a 

 necessity that the most favoured individuals will have the best 

 chance of surviving and leaving descendants, and by the law of 

 heredity, we know these offspring will tend to inherit the charac- 

 ters of their parents. This action is often spoken of as the 

 preservation of favoured races, and as the survival of the fittest. 



The gradual accumulation of beneficial characters will give 

 rise in time to new varieties and species ; and in this way primarily 

 has arisen the wonderful diversity of life that now exists. Such, in 

 barest outline, is the theory of descent with modification. 



Let us now see in what way this theory has been applied to 

 colouration. The colours, or, more strictly, the arrangement of 

 colours, in patterns is of several kinds, viz. : 



1. General Colouration, or such as appears to have no very 

 special function as colour. We find this most frequently in the 

 vegetable kingdom, as, for instance, the green hue of leaves, which, 

 though it has a most valuable function chemically has no particular 

 use as colour, so far as we can see. 



2. Distinctive Colouration, or the arrangement of colours in 

 different patterns or tints corresponding to each species. This is 

 the most usual style of colouring, and the three following kinds 

 are modifications of it. It is this which gives each species its own 

 design, whether in animals or plants. 



3. Protective Resemblance, or the system of colouring which 

 conceals the animal from its prey, or hides the prey from its foe. 

 Of this class are the green hues of many caterpillars, the brown 

 tints of desert birds, and the more remarkable resemblances of 

 insects to sticks and leaves. 



4. Mimetic Colouration, or the resemblance of one animal to 

 another. It is always the resemblance of a rare species, which is 

 the favourite food of some creature, to a common species nauseous 

 to the mimicker's foe. Of this character are many butterflies. 



c 



