566 Y. \y. (lAMJii.K. 



the case of green weed, the ])ackgTouiid is of a less luminous 

 character, the red colour contracts in tlie Hip))olyte and 

 the resultant coloration is then green, owing, in some cases, 

 to the presence of diffuse blue mingling with the yellow 

 network, and in the longest experiment to an apparent 

 change in the pigment from yellow to green. Tlie most iin- 

 ])ortant and most clear influence of red liglit, however, is the 

 spread of the yellow pigment. 



These results are so strikingly dissonant from those obtained 

 by subjecting Hippoly te to green or to red backgrounds that 

 an explanation is cleai'ly called for. They differ not only in 

 being totally opposed to the sympathetic colouring so charac- 

 teristic of the latter, but also in being slowly acquired. It 

 may fairly be asked, if red light reflected from red surround- 

 ings gives red Hippolyte, why does red light diffused give 

 green or yellow ones ? The same contradictory relation 

 obtains between the action of green surroundings and diffused 

 green light. 



In answer to this objection attention may be drawn to the 

 double natureof the light affecting Hippolyte under natural 

 conditions. There is the light i-ettected from the background 

 and there is also the general diffuse light. 



The rapid sympathetic background colour-relations obtained 

 experimentally have been made in strong daylight, and as the 

 depth of water is increased or as the red end of the spectrum 

 is cut off the conditions of the experiment are materially 

 altered. A stronorlv coloui-ed backo-round becomes black in 

 every light except that of its own colour, and in the presence 

 of it we should expect the usual black background effect 

 (brown, i.e. red and yelloAv pigments) to be produced in 

 Hippolyte in any light except that with which it agreed in 

 colour. But whilst this background effect is an undoubted 

 factor, its potency is determined by another factor, namely, 

 the definite action of diffused monochromatic light. The 

 action of many rays has yet to be determined, but from the 

 foregoing account a case has been made out for the action of 

 green and of red light. This action, though slow, is very 



