146 M. A.-E. Malard on the Influence of Light on 



likewise mimic to a deceptive degree, as I have very often 

 been enabled to observe, the ramifications of the algte on 

 which they are found. M. E. Chevreux ^ has already men- 

 tioned the singular adaptation which is exhibited in particular 

 by Caprella acutifrons to Cystocira granalata, the sea-weed 

 which is most often green with yellow spots (as at Les 

 Jonch^res, near the Croisic) ; the Caprella is seen to assume 

 the same colour and to cover itself with yellow spots of the 

 same shade and arranged in the same fashion ; while at other 

 points of the coast, where tlie alga3 are red, it assumes a 

 uniform brownish-red tint, identical with that of the sea- weed 

 upon which it lives (as at Bale d'Eslandes, near the Croisic). 

 For a long time it was believed that the food of the animal 

 was responsible for these changes in coloration ; but in a case 

 like the present it is very evident that, as M. Chevreux 

 remarks, the colour of the Caprella cannot be attributed to the 

 nature of its food t, since it is an exclusively predaceous 

 animal. It may be that we ought rather to regard this simi- 

 litude of form and colour as indicating a sort of rational act 

 on the part of the animal, which seeks a favourable place to 

 hide itself, and actually chooses the alga on account of its 

 shape, not adapting itself as regards colour until afterwards. 



In Hiiipolyte, a genus allied to Falwmon but of a slightly 

 smaller size, the adaptation of colour seems likewise to be 

 1 elated to the choice of habitat; thus Hippolyte varians, 

 which owes its name to these changes of coloration, will be 

 gieen in Zostera, brown in Fucus, red in Floridea, and trans- 

 parent or almost transparent when it is found SixmdiS.i Antennu- 

 loria and Sertulari'a. 



Now what is the cause of these changes of colour ? 

 It seems to be the same as that of the coloration of the 

 alga3. As a matter of fact experiments which have been made 

 upon this subject have proved that the same specimen of 

 Hip2)olyte assumes a red tint in complete darkness, while in 

 bright light it becomes a vivid emerald-green colour, and 

 semi-obscurity renders it brown. These experiments, which 

 I have myself repeated, would appear decisive. I am bound, 

 however, to state that I have met with a case which strangely 

 complicates the question. 



Thanks to the courtesy of the Board of Bridges and High- 

 ways (Buoying Service of the Arrondissement of Cherbourg), 

 and especially to the extreme kindness of M. Rouland, who is 



* E. CheTreux, * Les Plages du Croisic,' par Adrien Dolfuss, pp. 9 

 and 11. 



t Tbis remark had already been made iu the case of Iihtea by Mobius, 

 Bericht Exped. ' rommerauia,' p. 121. 



