288 SIGNIFICANCE OF SEXUAL REPRODUCTION [V. 



it is clear that the mechanism cannot have been developed 

 before the peculiar manner of holding the wings became ad- 

 vantageous to the butterfly, viz. before the similarity to a leaf 

 had made its first appearance. Conversely, this latter resem- 

 blance could not develope before the butterfly had gained the 

 habit of holding its wings in the appropriate position. Both 

 characters must therefore have come into existence simul- 

 taneously, and must have undergone increase side by side : the 

 marking progressing from an imperfect to a very close simi- 

 larit}', while the position of the wings gradually approached 

 the attitude which was exactly appropriate. The development 

 of certain minute structural elements of the central nervous 

 system, and the appropriate distribution of colouring matter 

 on the wings, must have taken place simultaneously, and 

 only those individuals have been selected to continue the 

 species which possessed the favourable variations in both 

 these directions. 



It is, how^ever, obvious that sexual reproduction will readily 

 afford such combinations of required characters, for by its 

 means the most diverse features are continually united in 

 the same individual, and this seems to me to be one of its most 

 important results. 



I do not know what meaning can be attributed to sexual 

 reproduction other than the creation of hereditary individual 

 characters to form the material upon which natural selection 

 may work. Sexual reproduction is so universal in all classes 

 of multicellular organisms, and nature deviates so rarel}' from 

 it, that it must necessarily be of pre-eminent importance. If 

 it be true that new species are produced by processes of se- 

 lection, it follows that the development of the whole organic 

 world depends on these processes, and the part that amphi- 

 gony has to play in nature, by rendering selection possible 

 among multicellular organisms, is not only important, but of 

 the very highest imaginable importance. 



But when I maintain that the meaning of sexual reproduction 

 is to render possible the transformation of the higher organ- 

 isms by means of natural selection, such a statement is not 

 equivalent to the assertion that sexual reproduction originally 

 came into existence in order to achieve this end. The effects 

 which are now produced by sexual reproduction did not 



