THE EELATION BETWEEN LIGHT AND PIGMENT-FORMATION. 578 



of young; red, colourless, or a mixed brood, containing red 

 and colourless individuals in the proportion of nearly 8:1. 



(3) This result suggests what is probable on other grounds 

 — that green Hippolyte are of two, and possibly of tliree 

 kinds: (1) Brown forms that have become green ; (2) green 

 forms that have undergone no change of colour; and (3) a 

 cross between these two. In the absence of knowledge of 

 the male parentage of the broods, the last suggestion needs 

 confirmation. 



(4) Light is not essential to the production of red pigment 

 in the larva. Darkness does not prevent the continued pro- 

 duction of red pigment in young forms. 



(5) The action of monochromatic light upon the pigment- 

 formation of Hippolyte is entirely different from that of a 

 monochromatic background in white light. 



(6) In pure red light, yellow pigment develops. In some 

 cases this leads to a green coloration : in others the colour 

 remains yellow. 



(7) In green light a carmine pigment is produced, and any 

 red or yellow pigment existing in the experimental batch is 

 either destroyed or disappears almost completely. 



(8) On a red background in white light, Hippolyte becomes 

 reddish-orange. 



(9) On a green background in white light, Hippolyte be comes 

 green, but the colour is not retained if the batch is transferred 

 to an absorbing dark background. 



(10) Continued exposure to daylight and a white back- 

 ground produces hypertrophy of the red pigment along the 

 nerve-cord and a disappearance of the red and yellow 

 pigment elsewhere. 



(11) The production of sympathetic colouring in the 

 shallower zones of the coast is explained as a background 

 effect, in which the incident diffused light plays little part. 

 The influence of background is predominant. The prod uction 

 of crimson colouring in deeper water is explained as due to 

 diffused green light. 



(12) There is no evidence that the pigments of the food 

 (alg£e) are the sources of the pigments of Hippolyte. 



