144 DARWINISM TO-DAY. 



colour-tone all brown individuals might disappear for some 

 special reason while both the lighter and darker individuals 

 might persist. Now if in consequence of this contrast a 

 racial feeling should develop between the light individuals 

 on the one hand and the dark ones on the other, the differ- 

 entiation into two species is already begun. If a snail species 

 living in fresh water is so harassed that it can only maintain 

 itself \vhen its individuals move either into the region be- 

 tween tide-lines or into the deeper water, this would lead to 

 morphological differentiation, as we can indeed actually note 

 in the case of the chitons." 



The objection that the existence of coadaptive and highly 



complex adaptations, especially those which seem as if they 



could be of no possible advantage to their pos- 



Answer to the sessors except in their present fully developed 



o ejection con- 

 cerning complex or specialised state, is one which. unfortunately 



ada P TaTions! ed cannot be definitely refuted or proved by ever 

 so much ingenious explaining or discussion in 

 the face of the lack of what we certainly do not now 

 possess, namely, direct observational or experimental evi- 

 dence. For such specialisations as elaborate mimickry, or 

 the electric organ of the torpedo, etc., which are of appa- 

 rent advantage only in perfected state, the selectionist is 

 forced to admit that the objector has apparently a good case, 

 but for the gradual specialisation of many highly complex 

 structures and specialisations through the long-continued 

 selection of slight advantageous variations, Darwin and his 

 followers have offered ingenious and plausible explanations. 

 For the case of so complex and coadaptive a specialisation as 

 the eye and its function in the vertebrates or in the insects 

 and crustaceans, the possible evolution, by slight additions 

 and modifications, from simple pigment fleck to the present 

 marvellous visual organ, a logically irrefutable Darwinian 

 argument can be made out on the basis of the real and 

 constant utility and advantage of even very slight steps 



