6 COLOR CHANGES IN ANIMALS 



though this may not conclude the list, leucophores and 

 iridocytes with their semi-crystalline or crystalline gua- 

 nin-like contents. These various types of chromato- 

 phores, partly through their own innate color exposures 

 and withdrawals, partly through their effects in covering 

 and uncovering other colored cells, combined also with 

 such physical light changes as are induced by the thin 

 transparent outer layers of the skin, have united to pro- 

 duce that marvelous play of animal colors which once 

 fed the eyes of the ancient Roman gourmands and which 

 now drives the modern biologist almost to despair. 



In 1852 Briicke published his important monograph 

 on the color changes of the African chameleon. In this 

 work he pointed out that when cutaneous nerves were 

 cut the denervated area of the skin made itself manifest 

 by darkening, that is, the dark pigment in the melano- 

 phores of this area became dispersed. Briicke expressed 

 the natural opinion that nerves severed in this way had 

 suffered paralysis and that the melanophores with which 

 these nerves were connected, having been released from 

 nervous control, lapsed into an inactive state. He 

 therefore regarded the stage of a melanophore with dis- 

 persed pigment as the relaxed or resting one as con- 

 trasted with that of concentrated pigment which he 

 believed to be the fully active stage. In this way he 

 brought chromatophores into line with ordinary muscle 

 fibers. This was a generalization of no small signifi- 

 cance and has been accepted by most later workers. 

 We shall see, however, that it may be open to question. 



In the early seventies of the last century the French 

 physiologist Pouchet (1872, 1876) carried out experi- 

 ments upon fishes similar to those that Briicke had per- 

 formed on chameleons. Pouchet cut integumentary 

 nerves and noted, for instance in turbots (Fig. 4), that 

 the denervated areas darkened as they had done in the 



