ORIGIN OF PIGMENT. 99 



final difficulty is the indispensable pre-existence of the pigment. 

 Whence and how does pigment originate ? Recent Darwinian 

 ! no more supply the answer to this question than the 

 older theories of the origin of colouring-matter through the 

 direct influence of light. It is incontestably certain that light 

 alone cannot give rise to a pigment, as was formerly supposed ; 

 and it is very probable that, even if the production of darker 

 colouring sometimes seems to depend on the influence of light, 

 it is to be attributed to the chemical rays or heat-rays which 

 are always associated with light-rays. It is equally certain that 

 all the peculiarities collectively which make animal pigments 

 useful to the owner do not make their existence indispensable ; 

 so that the chromatic function, in this special case, explains only 

 the various arrangements and rearrangements of pigment already 

 existing, but can throw no light on the obscurity which shrouds 

 the existence of these chromatophores, however great the utility 

 they may acquire, and undoubtedly possess, by the nature of 

 the different pigments they may contain and by their distribu- 

 tion and dependence on the eye and the optic nerve. 



The question remains equally unsolved with reference to 

 all other kinds of animal colouring. They may, as in the 

 chromatic function, be elicited and influenced by the indirect 

 action of the light, or they may, as is now very generally as- 

 sumed, have originated by natural or sexual selection; 29 but 

 these causes are still inadequate to the production of the pig- 

 ment itself, when we think of its origin irrespective of its 

 distribution. The eye was not formed by the faculty of sight, 

 although, when once it was formed, it was largely modified by 

 the function; the eye must have existed before it could be 

 used. The same is the case with regard to the pigment. I 

 lay some stress on this comparison, because it is so common to 

 find it stated in popular treatises, nay, often enough in scientific 

 works, that this or that colour is the result of selection or of 

 adaptation, the word 'colour' being no doubt used by many of 

 the writers instead of the more correct expressions colouring, 

 pittern or arrangement of colour. The answer to this ultimate 

 query How the pigment was first formed cannot at present 

 be given; and although many experiments and observations 



