REACTIONS OF MELANOPHORES OF AMBLYSTOMA 255 



tern is removed. The fact that Hertel ('07) obtained contrac- 

 tion of the chromatophores when he locally stimulated the skin 

 of Triton larvae with ultra violet rays is another matter, since 

 these rays probably always cause the pigment cells to con- 

 tract (Laurens, '15, p. 599). That he also obtained contraction 

 when he locally stimulated with yellow and red light, may be 

 due to one or more of several things. First, that the intensity 

 of the light was high ; second, since the light was focussed, that 

 the pigment cells were subjected to a high temperature; and 

 third, that the contraction of the pigment cells stimulated was 

 a reflex action. This last possibility has less in its favor than 

 the others, since there was no indication of spreading. Ballo- 

 witz's ('14) results of contraction are probably due to the effects 

 of the high intensity of the light that he used, about 1000 candles, 

 hardly to a heat effect (see p. 200). Moreover the melanophores 

 that he experimented with were taken not from the skin but from 

 the "Hirnhaut." Finally the results of Hooker ('12) are also, 

 it seems to me, capable of explanation.^ Hooker found, when 

 the melanophores of the frog (R. fusca) were completely deprived 

 of their nervous connections, either in the body or when bits of 

 skin were placed in hanging drop cultures, that for a day the 

 reactions of the melanophores w^ere the same as when they were 

 under normal conditions. But after this period of time had 

 elapsed the reactions of the pigment cells to light and darkness 

 were reversed. Hooker offers no explanation of this curious 

 fact. An explanation for the primary reactions, those lasting 

 for the first day, may be found in the fact that sunlight was used 

 as the source of light. It is therefore highly probable that the 

 contraction of the melanophores was a heat effect and not due 

 to the light at all. When the melanophores are placed in dark- 



' Opportunity is taken to call attention to the fact that Hooker is misquoted 

 on p. 598 of my former paper ('15) though rightly so on p. 628. Also that Ballo- 

 witz is incorrectly quoted on p. 598. The statement concerning his results 

 should read that when the melanophores are removed from the body they contract, 

 but when placed in salt solution they partially expand. When they are now 

 illuminated they contract. The opportunity is also taken to point out a mistake 

 in table 4, p. 589 where under 'black background' a II. reaction is indicated as 

 follows: "contraction (3-4 hrs.)" This should be struck out. 



