HIPPOLYTE VARIANS. 591 



or black colour^ and become colourless and transparent ; the 

 first named in the course of a few days, the Palsemon in a 

 few hours. Palaemon, moreover, was seen to pass through 

 a blue colour phase. 



These facts clearly indicated an interesting line of experi- 

 mental work, which Pouchet took up in the early seventies 

 with the most importaut and suggestive if not final results. 

 From 1872 he published a series of memoirs culminating in 

 that entitled ' Changements de coloration sous I'influence 

 des Nerfs ^ (1876), In this paper — by far the most im- 

 portant of those dealing with colour-change in Crustacea — 

 not only were the facts of colour mutability correlated for 

 the first time with changes of the pigment spots, but what is 

 much more important, the rationale of the change was 

 suggested as the result of experiments made at Costa's 

 zoological station at Concarneau on Pala9mon, Crangon, 

 and Hippolyte. 



Starting with the vague notions of fishermen, that fishes 

 and Crustacea change in colour according to the tint of the 

 sea bottom, Pouchet experimented with white and black 

 dishes, and found that Palaemon serratus (the form upon 

 which his results are chiefly based) alters its colour sympa- 

 thetically, becoming dark on a dark, colourless on a white 

 ground. This change is effected by the expansion and con- 

 traction of the pigment spots which are controlled by the 

 nervous system. By cutting off the eyes, a dark coloration 

 ensued, which remained unaltered until the eyes were re- 

 generated. The loss of the power of colour-change thus 

 appeared to be due to loss of sight, and the sequence of 

 events in a normal prawn was stated by Pouchet in these 

 terms (Conclusions, Nos. 17 and 18, p. 161) : 



" La fonction chromatique doit etre definie : un ensemble 

 d'actions reflexes sur les chromoblastes, dont le point de 

 depart peut etre I'impression visuelle resultant des proprietes 

 actiniques du milieu ambiant. Lesnerfs sontles conducteurs 

 de cette action reflexe : ils peuvent done provoquer I'expan- 

 sion ou le retrait des chromoblastes." The expression ''pro« 



