Reactions of Melanophores. 



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The reactions of the melanophores of amblystoma larvae. 

 By Henry Laurens. 



[From the Osbcrn Zoological Laboratory, Yale University.] 



The reactions of the sub-epidermal melanophores, in intact 

 and in isolated pieces of skin, to various stimuli, — light, tempera- 

 ture, solutions of various salts and drugs and electric currents — 

 were studied. 



The melanophores of normal and eyeless larvae 1 react to light 

 by expanding, and to darkness by contracting. If the normal 

 larvae are, however, kept in bright diffuse daylight on an in- 

 different background for more than 3 to 5 days the melanophores 

 secondarily contract. Likewise if they are kept in darkness for 

 more than 5 days the melanophores secondarily expand. These 

 secondary responses are lasting and are not shown by the melano- 

 phores of eyeless larvae. 



When larvae are blindfolded, instead of their eyes being removed, 

 the melanophores react to light like those of blinded individuals, 

 that is, they expand and remain so; but they react to darkness like 

 those of normal seeing larvae, that is, they at first contract, but 

 after 5 days or more they expand. 



The melanophores of isolated pieces of skin do not react to 

 daylight, to the light from a Nernst glower, or to darkness. The 

 light from an arc lamp, however, causes them to contract. 



From an additional series of experiments on larvae in which 

 the central nervous system had been partially or totally" destroyed 

 it is apparent that the primary responses of the pigment cells to 

 light and darkness are caused essentially by direct stimu- 

 lation. The secondary responses of the seeing larvae are, on 

 the other hand, due to nervous activities set up by the stimulation 

 of the retinae, the stimulation of sensory nerve endings in the 

 skin playing no part. 



A high temperature (above 38 0 ) causes the melanophores to 



1 The optic vesicles were removed from the larvae at the stage of develop- 

 ment when the tail bud is just appearing (see Laurens, Jour, of Exp. Z00L, XVI, 2, 

 p. 195, 1914). 



