146 M. A.-E. Malaril on the Influence of Lujht on 



likewise mimic to a doceptive degree, as I liave very often 

 been enabled to observe, the ramifications of the algfe on 

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

 tioned the singular adaptation which is exhibited in particular 

 by CaprcUa acutifrons to Cystocira granulata, the sea-weed 

 ■which is most often green with yellow s|)ots (as at Les 

 Joncheres, near the Croisic) ; the Cnprella 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 

 ]ioitits of the coast, where the algai are red, it assumes a 

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

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

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

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

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

 Vi'marks, the colour of the Caprella cannot be attributed to the 

 nature of its food f, 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 Uippolytej a genus allied to Pahtmon but of a slightly 

 sn;aller size, the adaptation of colour seems likewise to be 

 lelated to the choice of habitat; thus Hippolyle varians^ 

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

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

 ])arent or almost transjiarent when it is found amidst An ten nu- 

 laria 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 

 algte. Asa matter of fact experiments which have been made 

 upon this subject have proved that the same specimen of 

 Jjipjwh/te assumes a red tint in comj)k'te darkness, while in 

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

 semi-obscurity renders it brown. These experiments, which 

 1 have myself repeated, would appear decisive. 1 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. liouland, who is 



• E. Chevreux, * Les Plages du Croisic,' par Adjim Dolfiiss, pp. 9 

 and 1 1 . 



t Tliis remark had already b«cii made in the case oi Idotca hy Mcibius, 

 iJtiiclit J-lxjiL'd. ' roiunuTania,' p. \'2\. 



