HIPPOLYTE VARIANS. 593 



red colour in the dark. If it was then replaced in the 

 light the red colour disappeared. Jourdain concludes 

 (loc. cit., p. 302), " des lors au moins lorsq'on I'etudie en 

 captivite le Nika n'a pas la meme couleur la nuit que le 

 jour," but he does not appear to have made any observations 

 at night to verify this. Jourdain also found that if the tem- 

 perature is lowered to 5° or 6° C. the colour-changes are 

 effected more slowly. In the case of specimens in which the 

 eyes had been removed, the colour became and remained 

 red at normal temperatures, was ultimately lost at or near 

 0° C, but returned if the water was warmed, and also 

 when the eyes regenerated. Eye-amputated specimens ex- 

 posed to very bright light for some time lost some of their 

 red colour ; but in all these experiments a certain number 

 of the prawns behaved in a different manner. 



On the subject of the present work — Hippolyte varians 

 — but little experimental evidence has been collected. Beyond 

 the single result that, on a dark ground, green Hippolyte 

 became reddish brown, Pouchet had little to record. More 

 recently, however. Professor Herdman (1892, 1893, 1898), 

 Mr. Hornell (1897), and M. Malard (1893) have made trials 

 to test the colour mutability of this species on differently 

 tinted weeds. Professor Herdman concluded (1898) "that 

 Hippolyte varians can change its colouring, though not 

 in a very short space of time,'^ but the change was not a 

 close match with the tint of the new weed. Mr. Hornell 

 concludes from experiments at Jersey that a power of sympa- 

 thetic colour-change is equally well shown in the light and 

 in the dark. We have ourselves made the observation that 

 even when the AlgaB are changed in the dark, a colour- change 

 occurs which in some cases may match the tint of the new 

 weed ; and we offer an explanation of the apparently remark- 

 able phenomena in the section on recovery from the nocturnal 

 colour (Sect. IV, pp. 614 and 616). 



M. Malard (1893) found that green Hippolyte become red 

 in the dark, but he does not appear to have followed up this 

 observation by experiments at night. 



