428 APPENDIX 



stripes, which occur on the skins of animals has been under- 

 valued in a quite extraordinary way. It has been the 

 custom to consider all this as of no importance, and no one 

 has thought of looking in any way for the law^s which govern 

 these phenomena and the connection between them. But by 

 attentive examination I found that these characters followed 

 most wonderfully definite laws, that there is no point in the 

 marking of any animal which has not a quite special and 

 definite typical importance, and that among all the markings 

 which occur on the surface of the animal-body a high degree 

 of connection is to be recognised. Thus there are different 

 types of marking which pass by gradual modifications one 

 into another, so that, when the extreme forms of such mark- 

 ings are connected by the intermediate forms, those which 

 are apparently most different can be brought into a connected 

 relationship. 



For example, if we place together all the Lepidoptera 

 which belong to one group, the butterflies, we shall find 

 that there are surprising connections between one species 

 and another, between this and a third, and so on ; connec- 

 tions which point to the perfectly gradual modification of 

 the species according to the plan of arborescent ramification, 

 and to the fact that the cause of this depends on the varia- 

 tion of the species, in other words of the individual, in 

 perfectly definite directions. The species varies here and 

 there, but only in a few perfectly definite details, and 

 usually in one direction only. There appears on the wing, 

 for instance, first a new minute streak as a darkening in a 

 perfectly definite position ; on a second sjDecimen of the same 

 species it is larger and shows whither the evolution will lead. 

 In the most nearly allied species it forms a constant con- 

 spicuous diagnostic character, in the next it is still more 

 altered in the direction indicated, perhaps accompanied by 

 another new variation appearing for the first time. So we 



