564 F. W. (iAMBLE. 



'i'he results are shown on Table A, and at once bring out 

 the fact that colourless muscle, white or red, ova are greedily- 

 taken up, but that the background is the dominating factor in 

 the resultant coloration in daylight. Thus against a back- 

 ground of green weed Hippolyte fed with colourless food, 

 with red ovary, and with fine brown weed became green. In 

 darkness, however, the amount of pigment in the food has 

 a rough relation to the resulting colouring that will need 

 furtiier experimental testing, but there is no good evidence 

 that the colour of the food determines that of the prawn. 



V. Analysis of the Coloured Light Experiments. 



(1) In green light, and amongst red weed, Hippolyte 

 develops crimson and deep, not superficial, colouring. 



The presence in the experimental vessels of a fair quantity 

 of finely branclied red weed (Ceramium) would, under the 

 action of diffused, strong green light act as a black back- 

 ground, and this, as we know, in the presence of white light, 

 encourages the formation of vermilion and yellow pigments, 

 and these are most notably absent. 



The crimson effect in green light cannot, therefore, be 

 merely due to dim light acting on a dark background. It 

 must be due to a distinctive factor not present in the other 

 experiments, and that factor can only be the green rays. In 

 the presence of these rays, not only is the crimson pigment 

 developed, but the vermilion and yellow pigments are dis- 

 missed. Whether a similar result would follow if a colour- 

 less food were used is of course a subject for further research. 



The most striking feature of this crimson colouring obtained 

 during exposure to green light, is the fact that it is comple- 

 mentary in colour to that of the incident light. This rehition 

 may have a considerable significance. In an earlier paper 

 (1905) it was pointed out that strongly iusolated Hippolyte 

 showed mobile fat in their chromatophores, and as this fat 

 disappeared in specimens transferred to darkness there was 

 some ground for the inference that the production of this 



