466 ORIGIN OF SPECIES 



icked forms, can be shown by a graduated series to be merely 

 varieties of the same species; whilst others are undoubtedly 

 distinct species. But why, it may be asked, are certain forms 

 treated as the mimicked and others as the mimickers? Mr. 

 Bates satisfactorily answers this question, by showing that 

 the form which is imitated keeps the usual dress of the group 

 to which it belongs, whilst the counterfeiters have changed 

 their dress and do not resemble their nearest allies. 



We are next led to inquire what reason can be assigned 

 for certain butterflies and moths so often assuming the dress 

 of another and quite distinct form; why, to the perplexity of 

 naturalists, has nature condescended to the tricks of the 

 stage ? Mr. Bates has, no doubt, hit on the true explanation. 

 The mocked forms, which always abound in numbers, must 

 habitually escape destruction to a large extent, otherwise 

 they could not exist in such swarms; and a large amount of 

 evidence has now been collected, showing that they are dis- 

 tasteful to birds and other insect-devouring animals. The 

 mocking forms, on the other hand, that inhabit the same dis- 

 trict, are comparatively rare, and belong to rare groups; 

 hence they must suffer habitually from some danger, for 

 otherwise, from the number of eggs laid by all butterflies, 

 they would in three or four generations swarm over the 

 whole country. Now if a member of one of these perse- 

 cuted and rare groups were to assume a dress so like that of 

 a well-protected species that it continually deceived the prac- 

 tised eyes of an entomologist, it would often deceive preda- 

 ceous birds and insects, and thus often escape destruction. 

 Mr. Bates may almost be said to have actually witnessed the 

 process by which the mimickers have come so closely to re- 

 semble the mimicked; for he found that some of the forms 

 of Leptalis which mimic so many other butterflies, varied in 

 an extreme degree. In one district several varieties oc- 

 curred, and of these one alone resembled to a certain ex- 

 tent, the common Ithomia of the same district. In another 

 district there were two or three varieties, one of which was 

 much commoner than the others, and this closely mocked 

 another form of Ithomia. From facts of this nature, Mr. 

 Bates concludes that the Leptalis first varies; and when a 

 variety happens to resemble in some degree any common 



