70 



Colouration in Animals and Plants. 



hues is as beautiful as it is convincing. None can doubt the love 

 of display exhibited in such actions. 



The deliuacy of their organization renders butterflies peculiarly 

 susceptible to any change, and hence they exhibit strong tendencies 

 to variation, which make them most valuable studies. Not only do 

 the individuals vary, but the sexes are often differently coloured. 

 Where two broods occur in a season they are sometimes quite 

 differently decorated, and finally a species inhabiting widely different 

 localities may have local peculiarities. 



We can thus study varieties of decoration in many ways, and we 

 shall treat of them as follows : — 



1. Simple Variation, in which the different individuals of a 



species vary in the same locality. 



2. Local Variation, in which the species has marked peculiarities 



in different localities. 

 Sexual Dimorphism, in which the sexes vary. 

 Seasonal Dimorphism, in which the successive broods differ. 

 In order fully to understand the bearing of the following remarks 

 it is necessary to know something of the anatomy and nomencla- 

 ture of butterflies. Fig. 3 is an ideal butterfly. The wing margins 



3. 

 4. 



Diagram of Butterfly's Wing. 



/. Costal nervure. 



g. Sub-costal do. 

 g Ui . Branches of do. 



h. Median nervure. 



i. Sub-median do. 



j. Discoidal Cell. 



k. Discoidal Veins. 



