On the Seasonal Dimorphism of Butterflies. 101 



can scarcely be doubted that new species can be 

 formed in the manner indicated ; and I believe 

 that this was and is still the case, with butterflies 

 at least, to a considerable extent ; the more so 

 with these insects, because the striking colours and 

 markings of the wings and body, being in most 

 cases without biological significance, are useless for 

 the preservation of the individual or the species, 

 and cannot, therefore, be objects of natural selection. 



Darwin must have obtained a clear insight into 

 this, when he attempted to attribute the markings 

 of butterflies to sexual and not to natural selec- 

 tion. According to this view, every new colour 

 or marking first appears in one sex accidentally, 1 

 and is there fixed by being preferred by the other 

 sex to the older coloration. When the new or- 

 namentation becomes constant (in the male for 

 example), Darwin supposes that it becomes trans- 

 ferred to the female by inheritance, either partially 

 or completely, or not at all ; so that the species, 

 therefore, remains more or less sexually dimor- 

 phic, or (by complete transference) becomes again 

 sexually monomorphic. 



The admissibility of such different, and, to a 

 certain extent, arbitrarily limited inheritance, has 

 already been acknowledged. The question here 

 concerned is, whether Darwin is correct when he 



1 [" Accidental " in the sense of our being in ignorance of 

 the laws of variation, as so frequently insisted upon by Darwin. 

 R.M.] 



