THE KELATION BETWEEN LIGHT AND PIGMENT-FOKMATION. 565 



fat was associated with the presence of light. If that were 

 so the assumption of a complementary colouring would be 

 obviously the best means of absorbing the maximum amount 

 of coloured liglit^ and of obtaining any other benefit which 

 light might confer upon metabolism. Under the conditions 

 of deep water, where the green or gi-eeu-blue rays have 

 filtered down from the sui-face, such a colouring would be the 

 most efficient absorbing pigmentation, and it is well known 

 that in hauls made from the deeper water of the English 

 Channel the Hippolyte are uniformly of a crimson colour. 



The facts as to these crimson Hippolyte produced in green 

 light would be most comprehensively explained by saying 

 that the red Ceramiuni acted merely as an excitement to 

 coloration, but that the carmine pigmentation is produced 

 under the direct stimulus of the green light employed, 



,o\ r Green weed . Green coloration . Superficial and deep. 

 Tj }y 1 ■ < Red weed . Yellow or hrownish- cliromatopliores. 

 *^ (. yellow 



The action of red light is less easily analysed. The constant 

 effect associated with it, is the production of yellow pigment 

 and the maximal expansion of that pigment into networks 

 producing a grand colour. Then, according to the absorbent 

 or reflecting natui-e of the background (i,e. green weed or 

 red weed), we have a green or a brownish tint, in the latter 

 case accompanied by a development of scarlet chromato- 

 phores both at the surface and along the lines of the 

 alimentary tract and of the nerve-cord. 



In the case of red light, therefore, it would seem that the 

 direct action of the rays lies in the production of yellow 

 pigment, and that the nature of the background, indirectly 

 modified by the further action of the red light, modifies this 

 yellow coloration less or more. If the background be red. 

 the action of the rays is intensified, and a red background is 

 thus instituted. Probably this is the factor that gives the 

 scarlet chromatophores, for, as will be seen subsequently, 

 that is the effect of a red backsrround in white lig-ht : the 

 resultant colour is then brownish-yellow ; but where, as in 



VOL. 55, PART 3, — NEW SEKIPJS, 37 



