BUTTERFLIES AND MOTHS 



Batesian mimicry. The combined advertisement was inter- 

 preted some years later by Fritz Miiller and is called MQl- 

 lerian mimicry. 



I hope that the above paragraph makes clear the advantage 

 that would be gained by a species whose pattern resembled 

 that of another species which was not eaten by birds. Prob- 

 ably we should have an excellent opportunity of actually wit- 

 nessing evolutionary progress if we could compare one imper- 

 fect mimic in such a group with what it was a hundred years 

 ago. A century is only a drop in the ocean of time, but even 

 in this short period some notable change might be evident. 

 Well, we are fortunate enough to be able to make this 

 comparison. 



Between the years 1825 and 1830 the great naturalist Wil- 

 liam John Burchell was travelling in eastern Brazil, making 

 extensive collections of animals and plants, concerning which 

 he made the most accurate and detailed notes. I only wish 

 that all naturalists to-day would do their work as well. His 

 whole collection of insects is in the Oxford University 

 Museum, and among them are many butterflies belonging to 

 the great yellow-banded group of which I have spoken. In a 

 certain species known as Lycorea halia, the yellow band along 

 the hind wing is not so bright as in other species of the group, 

 and the eight specimens in the Burchell collection show that 

 this characteristic feature was on the average even less bright 

 a hundred years ago. It may be suggested that the colours 

 have become darker with age; but with age butterfly pigments 

 generally become paler rather than darker. Besides, among 

 the eight there is one that is fairly bright, though by no means 

 equal to the brightest of to-day, whereas among specimens 

 recently caught a small proportion resemble the seven that 

 are not so bright. The evidence that the colour has changed 

 slightly in a hundred years is, I think, unquestionable. 



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