n LAWS OF VARIATION 29 



appear behind. (Law of wave -like evolution, or law of 

 undulation.) 



4. That the whole of the varieties and variations of a 

 species represent nothing else but stages of the course of 

 development passed through by the individuals of the species 

 unless they represent new characters usually appearing 

 first in males. One variety will thus stand at stage a, another 

 at stage b, and so on ; but one or another is possibly dis- 

 tinguished by a new character, e. 



But in the same direction as the peculiarities of the 

 varieties lie those which characterise the related species. The 

 species most nearly related may, for example, present the 

 varieties /, g, h, i. The character e, which occasionally appears 

 in the previous species, is the most characteristic peculiarity 

 of the second species the variation of the first towards e 

 showed already the direction in which evolution proceeds 

 farther. In the second species appears occasionally a character 

 k, which has the same significance as e had before, and so on. 



So, if one examines numerous individuals of a species with 

 regard to its variation, he can in the clearest manner in many 

 cases show from this variation its relation to other species. 1 

 As I said in my Freiburg address, the evolution the growth 

 of species one from another proceeds onwards as though 

 following a plan drawn out beforehand. In the case supposed 

 if all the stages of evolution from a to i were of equal import- 

 ance, we should unite them all together as varieties of a single 

 species ; but if between a and i one stage is altogether wanting, 

 or if one of them, say in the second half of the series, appears 

 suddenly with special prominence, dominant, then we have, 



1 For the clearer comprehension of this compare the details in my paper 

 already cited, Ueber das Variiren, etc., with the figures and the last sections. Also 

 my work with coloured plates shortly to be published by G. Fischer in Jena, 

 Die Schmetterlinge nach ihrer auf die Zeichnung begriindete Verwandtschaft 

 dargestellt und beschrieben. Lastly, my illustrated articles, Ueber die Zeichnung 

 der Saugethiere, in the last three years of the journal Humboldt. 



