178 Darwin, and after Darwin. 



affected are not exposed to the view either of enemies 

 or of prey. 



Analogous illustrations to any amount may be drawn 

 from Mammals. For instance, I have worked through 

 the Marsupials with the aid of Mr. Oldfield Thomas' 

 diagnostic description of their numerous species. 

 Now, let us take any one of the genera, such as 

 the kangaroos. This comprises 23 species living on 

 an island continent of high antiquity, and not ex- 

 posed to the depredations of any existing carnivor- 

 ous enemies ; so that there is here no present need 

 to vary colour for purposes of protection. More- 

 over, in all cases the diagnostic distinctions of 

 colour are so exceedingly trivial, that even if large 

 carnivora were recently abundant in Australia, no one 

 could reasonably sug,<4est that the differences in 

 question would then have been protective. On an 

 average, each of the 23 species presents rather more 

 than 20 peculiarities of shading, which are quoted 

 as specifically diagnostic. Altogether there are 474 

 of these peculiarities distributed pretty evenly among 

 the 23 species ; and in no case can I conceive that 

 utility can be suggested. 



Hitherto we have been considering the question of 

 fact, as to whether "a large proportional number 

 of specific characters " do or do not admit of having 

 their utility demonstrated, or even so much as plaus- 

 ibly suggested. In the result, I can only conclude 

 that this question of fact is really not an open one, 

 seeing that it admits of an abundantly conclusive 

 answer by any naturalist who will take the trouble 

 to work through the species of any considerable 



