558 V. W. aAMBl;E. 



cliieriy with short exposures made upon an absorbing or re- 

 flecting background. The results showed that the light acted 

 irrespective of its colour according to the nature of the back- 

 ground, almost as though it were white light of low intensity. 

 Moreover, experiments with coloured backgrounds of weed, 

 against which young, transparent, al most colourless H i p p o 1 y t e 

 were exposed to direct sunlight, showed (1905, see Tables) 

 that in two days, eleven out of fifteen prawns became red on 

 red weed, and eight out of twelve became green on green 

 weed. The coloured backgrounds, when flooded with white 

 light, produced sympathetic colouring. The red was a 

 mixture of red and yellow, the former predominating, the 

 green a mixture of the same two pigments but yellow pre- 

 dominating. In both cases a difluse blue pigment occurs also. 



This result appeared to lend some support to the view of 

 Wiener (1895) (which has since undergone elaboration 

 [Bachmetjew, 1908] ), and to suggest that the dominant rays 

 of the background evoked especially that pigment or that 

 group which agreed in colour with the reflected light. 



In order to ascertain more fully the effect of monochromatic 

 light, ] determined to eliminate, as far as possible, this 

 dominant influence of background, and to ascertain the 

 result of exposure to incident light of one colour. So far as 

 I am aware, the experiment in this form has not hitherto 

 been undertaken. The starting-point for this experiment 

 was furnished by young transparent Hippolyte varians 

 taken by netting over Zostera beds and Laminaria-fringes. 

 These fall into two groups : typical faintly red-lined forms 

 provided with red and yellow chromatophores along the gut 

 and nerve-cord, and with red ones at segmental intervals in 

 the integument ; and more uniformly coloured specimens 

 with similar pigments, but with chromatophores more evenly 

 distributed. In both cases the amount of pigment is not 

 enough to give the specimens a decided tinge. They are 

 similar to those used for the weed background experiments 

 quoted above, and are figured on PI. 23, fig. 4. 



The vessels which were used are described above (p. 554), 



