JOURNAL OF VARIATION. 



Vol. VIII. No. 1. May 1st, 1896. 



MIMICRY. 



1. — General observations. Selection. Protective coloration. 



Utility. 

 By J. W. TUTT, F.E.S. 



Every educated man and woman has heard of the leaf -butter- 

 flies, and, sooner or later, every entomologist, when showing his 

 collection to a friend, is suddenly pulled up and asked to explain why 

 certain insects resemble leaves, and how such peculiarities have arisen. 



There are three ways of answering the enquirer's question, so far 

 as Ave have observed : — (1) To say you do not know. (2) To equivocate, 

 because you do not like to say you do not know. (3) To explain the 

 matter clearly to your own satisfaction and that of the enquirer. 



In order to do the latter, even in general terms, it is necessary to 

 have some definite idea as to details one's self. The reason why 

 certain insects resemble leaves is evident : it is to enable them to 

 escape from enemies that would otherwise prey upon them. To explain 

 how the peculiarities, which give them such strong resemblances to 

 leaves, have arisen, is a much more difficult matter. 



It is evident that, if we are to attempt to explain the matter, we 

 must hazard a theory. Our theory, it must be remembered, only 

 attempts to explain the facts. The use of a theory is to offer a 

 probable explanation. If it explains all the conditions we observe, it 

 may be that the theory is really the true explanation of how the 

 facts have been brought about. So soon as the theory ceases to be in 

 accordance with observed facts, so soon the theory must be discarded. 



Those who have attempted to explain the origin of mimicry have 

 done so from two diametrically opposite standpoints. The first, as 

 exemplified by Darwin and Wallace, have looked upon the external 

 forces of natural selection as the cause. Others, as Niigeli and 

 Askenasy, have looked upon it entirely as the result of forces at work 

 within the organism. 



Neither of these alone entirely satisfies the conditions, but a 

 combination of the action of certain internal forces, with the principles 

 of natural selection as enunciated by Wallace and Darwin, gives a very 

 satisfactory explanation of the phenomena observed. It appears to 

 us that internal forces must be considered as giving rise to variations 

 of the structure, so as to allow of the necessary modifications. The 

 internal force is, therefore, in a manner, creative. The external 

 force acts selectively on the organism, and determines the particular 



