240 THE COLOURATION OF INSECTS 



posing that a mimic was produced suddenly in the likeness 

 of some other species, by a large variation known as 

 a mutation, and that the Mendelian principle perpetuated 

 this unchanged, the pattern, etc., being due to presence 

 or absence of certain " factors," or of factors inhibiting 

 others. 



. If mimics are produced by mutations, it is remarkable 

 that not only superficial aspect, but movements and habits 

 should be produced that, quite fortuitously, are extra- 

 ordinarily like those of some other species in the same 

 neighbourhood, and it seems highly remarkable that such 

 mutations should resemble species of the type described 

 as aposematic. How is it that mutation does not pro- 

 duce new forms resembling procryptic species 1 Why 

 should all the females of P. dardanus be modified by 

 mutation to resemble different species of conspicuous, 

 relatively distasteful butterflies of genera belonging to 

 two different sub -families ? Why has not a form of the 

 excessively variable species Pseudacraea eurytus (see next 

 chapter) been produced that deceptively resembles some 

 procryptic species 1 This most wonderful genus has 

 only two out of over a score of forms that are not close 

 copies of some other butterfly, and yet the species 

 resembled are all aposematic ! It seems incredible that 

 mutation can produce only pseud-aposematic variation. 

 Where, then, are the other less conspicuous forms ? No 

 other conclusions seem possible than that they have 

 been destroyed by enemies before they could establish 

 themselves. If this be so, the argument that insectivorous 

 enemies do not destroy butterflies in sufficient numbers 

 to have a selective influence falls to the ground. 



As a matter of fact, a few cases are known of such a 

 Variety differing very considerably from its parents to 

 a degree that could be claimed as an instance of the 

 sudden appearance of a mutation. ^ But they are ex- 



1 Bedrock, vol. i, pp. 63-4 — an example of a rare large variation in 

 Acraea alciope. 



