192 THE COLOURS OF ANIMALS 



The similarity has arisen from the fact that the 

 species in each group are closely related, so that 

 natural selection has maintained an initial resem- 

 blance, instead of causing convergence, as it has done 

 with more distantly related species. Hence repetition 

 of the same appearance may be produced by a pre- 

 vented divergence, as in these cases, or by the actual 

 convergence of forms originally unlike, as in the former 

 cases. 



The convergent forms are more perfectly con- 

 spicuous, more ideally warning, because they have 

 been further modified from their original appearance ; 

 while the forms in which divergence has been arrested 

 have merely adopted, with comparatively slight modi- 

 fication, an appearance which was produced by the 

 operation of other principles, but which is sufficiently 

 well known for the purpose. 



These interesting conclusions have gradually grown 

 out of the observations of many naturalists. 



The arrested divergence, sometimes aided by actual 

 convergence, has produced such remarkable resem- 

 blances between certain species of unpalatable insects, 

 that Bates speaks of the wonderful fact that such 

 species mimic each other. Wallace at first looked 

 upon these mysterious resemblances as due to some 

 unknown cause connected with locality, for the 

 sunilar species are nearly always found together. 



The difficulty was at length explained by Fritz 



