410 



them to bear upon their peculiar views respecting the classificiitiou 

 of animals. It is to Mr. Bates, and to his observations on the 

 butterflies of S. America, embodied in an able and elaborate paper 

 in the Linnean Transactions* that we are indebted for those 

 details on the subject which have given it so much attraction of 

 late years, and which have led to a reconsideration of the causes 

 to which mimicry may be attributed and the object of its existence. 

 Darwin and Wallace have followed in the inquiry, the latter 

 gentleman especially testing, by the results of his own observations 

 in the Malay Archipelago, the correctness of the theory by which 

 Mr. Bates would explain the circumstance. The explanation rests 

 on the belief that the imitation is for protective purposes, and that 

 it is gradually brought about by natural selection seizing hold of 

 any little accidental variations in the form or colouring of the 

 mimicker, by which it makes the slightest approach towards the 

 species mimicked, and constantly increasing the variations in 

 that direction until the two species are outwardly similar. The 

 mimicked and mimickers are almost always found together in " the 

 same district, and in most cases on the very same spot ;" the former 

 being in much larger numbers than the latter. Mr. Wallace 

 observes " that the forms imitated always belong to dominant 

 groups, or those excessively abundant in species and individuals, 

 and therefore presumptively free from the attacks of those insect- 

 enemies that keep down the numbers and threaten the extinction of 

 other species." In some cases it is thought to be a powerful odour 

 emitted by species enjoying this immunity which serves for their 

 protection. Where this is the case, other species not possessing 

 this odour, and therefore more often falling a prey to birds, would 

 have great advantage in assuming the colour and markmgs of the 

 species mimicked so as to be mistaken for it, and to escape being 

 devoured. 



For further illustration of this subject the reader is referred to 

 Mr. Wallace's book on " Natural Selection," where ample details 

 are given, t All the most striking cases of mimicry among the 

 Lepidoptera hitherto recorded are from the tropics. Not many 



* Liim. Trans., vol. xxiii , p. 495. t Contributions to the Theory of 



Natural Selection, p. 75, &c. 



