70 



well on the way to the form becoming a specialised local 

 race, responding by means of a peculiarity in organisation 

 to a peculiarity in environment, and thus a distinct step 

 towards its becoming a distinct species. On the other hand, 

 one might ask whether this yellow coloration, being the 

 expression of a slight change in the organism itself due to 

 environment, and of value to the species under those peculiar 

 environmental conditions amongst which it persists, indi- 

 cates any greater step in the direction of a new species than 

 does the development of a dark race of Gnophos obscurata on 

 peat, and of a white one on chalk soils. 



I would answer that it does not indicate a greater step, 

 because I am firmly convinced that specialisation to the 

 complex conditions of a particular environment is the great 

 factor in the development of specific forms, and in both 

 cases instanced the changed conditions of environment have 

 apparently resulted in a modification of physiological func- 

 tion, in one of which the result has been the change of a 

 red into a yellow pigment, whilst the other has resulted in 

 the production of a greater number of black (on peat) or 

 white (on chalk) scales. That these specialisations are 

 mainly judged by naturalists by the external appearances of 

 form and colour does not alter the fact that they are essen- 

 tially manifestations of varying conditions of function in the 

 organism, the external appearances being moulded by their 

 utility to the preservation of the species in its respective 

 stages. I was much struck, therefore, to read in the 

 " Materials for the Study of Variation" that " the differences 

 between species are specific, and are differences of kind 

 forming a discontinuous series ; whilst the diversities of 

 environment to which they are subject are, on the whole, 

 differences of degree, and form a continuous series. It is, 

 therefore, hard to see how the environmental differences 

 can thus be in any sense the directing cause of specific 

 differences, which, by the theory of natural selection, they 

 should be." 



It may be well to examine this carefully. It is quite true 

 that if we compare species such as Dryas paphia and Argynnis 

 adippe, Apatura iris and A. ilia, the differences between 

 them are specific and differences of kind ; but can we say 

 that their respective environments, even if inhabiting the 

 same wood, are not just as different in kind? But if we 

 consider a group of organisms such as Anthrocera lonicerce, 

 A. mcdicaginis, A. trifolii, A. palustris, and A. seriziati, how 

 far is this statement true? Certain groups of Erebia, 



