20 COSMIC FBILOSOPHY. [pt. ii, 



animal, which in turn will modify its speed, its muscular 

 (levelopmeut, its mental faculties, and its habits of life. 



Having- thus briefly indicated the capacity of the theory of 

 natural selection for explaining the most general phenomena 

 of organic variation, let us in conclusion observe how admir- 

 ably it explains certain special phenomena, which do not 

 otherwise admit of scientific explanation. For evidence of 

 the signal success with which Mr. Darwin has explained 

 such otherwise unaccountable facts as the dimorphism of 

 certain flowers, the existence of neuters or sterile females 

 among bees and ants, the odoriferous glands in mammals, 

 the calcareous shells of mollusks, tlie heavy carapace of the 

 tortoise, the humps of the camel, the amazingly complicated 

 contrivances through which orchidaceous plants are fertilized 

 by insects, the slave-making instinct of certain ants, the 

 horns of male ruminants, and countless other phenomena ; 

 for all this, I must refer to Mr. Darwin's various works. 

 From the mass of phenomena to which the theory of natural 

 selection has been satisfactoril}'^ applied, I will only select 

 as an illustration the case of colour, in the animal and 

 vegetal kingdoms. 



Until after the publication of Mr. Darwin's speculations, 

 the colours of plants and animals had never been made the 

 subject of careful and philosophical study. So far as any 

 hypothesis was held concerning these phenomena, it was the 

 vaguely conceived hypothesis that they are due to the direct 

 action of such physical conditions as climate, soil, or food. 

 But there are fatal objections to such an explanation. When 

 Dr. Forbes Winslow, in his work on the " Physiological 

 Influence of Light," tells us that " the white colour of ani- 

 mals inhabiting the polar regions is attributable to the 

 absence of intense sunlight," it is an obvious objection that 

 the polar regions are not pre-eminent for darkness. Though 

 within the limits of the arctic circle the sun is below the 

 horizon for six months together, it is none the less for the 



