A CAUTION 147 



the caution that insects in their perfect state 

 do not grow, and that if we find two butterflies 

 similar in appearance but differing considerably 

 in size, we may assume that they are different 

 species. I haye certainly seen considerable 

 differences in size in single specimens. I have 

 two puss moths, one of which is half as big 

 again as the other, but such instances are 

 exceptional. The practical principle is this 

 a small butterfly will not grow into a 

 larger one. 



The common white butterflies are old 

 friends. Whether we spent our childhood 

 in town or country, one of our earliest 

 recollections is the sight of those soft, white- 

 winged creatures in the parks and gardens 

 of the one, or in the fields and hedgerows of 

 the other. Next to the birds, they were the 

 largest flying objects we saw, and they became 

 the source of much exciting sport. As we 

 seldom caught them, it is possible that the 

 insects also regarded the pursuit in a 

 sporting way. 



I remember, when very young, going out 

 to a field of hay in the early morning and 

 picking the small white butterflies off the 



