206 HENRY LAURENS 



took place in the retinae of frogs when only the skin was exposed 

 to light; though Fick ('90) obtained results which led him to 

 conclude that interference with the normal respiration was the 

 cause of these changes. Koran3d ('92) noted that illumination 

 of the skin caused microscopic changes in the retina similar to 

 those produced by illumination of the eye itself. In my results 

 there is also an indication that there is such a connection between 

 the nerve terminations of the eyes and of the skin. As has been 

 pointed out there is a difference in the condition of the skin pig- 

 ment of normal and blinded larvae under the same conditions of 

 illumination and background. If normal larvae are placed in dif- 

 fuse light on a white background they become pale (that is, the 

 pigment in the skin chromatophores contracts) ; if blinded larvae 

 are placed under the same conditions, they become dark (that is, 

 the pigment expands). If normal larvae are placed in darkness 

 they become dark; if blinded larvae are placed in darkness they 

 become pale. If normal larvae are placed in diffuse light on a 

 black background, they become dark, if blinded larvae are so 

 placed they also become dark. In only this last case then of 

 placing normal and blinded larvae in diffuse light on a black 

 background are the same conditions of the skin pigment obtained. 

 As we have seen however, in the blinded larvae, the nature of 

 the background is of no unportance, since both white and black 

 backgrounds in diffuse light produce the same results, light and 

 darkness being the only factors to be considered in the case of the 

 blinded individuals. Normal larvae, on the other hand, show 

 different conditions of pigment when placed in diffuse light on a 

 white and on a black background. It would seem fair to con- 

 clude then that there must be some connection between the 

 nerve terminations of the two light receptors, the eye and the 

 skin, since in the larvae in which the eyes are left intact a differ- 

 ent condition of the pigment of the skin is obtained from that 

 which is found in the bUnded larvae under the same conditions 

 of illumination and background. 



For the experiments which have been so far described none of 

 the Amblystoma larvae were under 15 mm. in length. They all 

 showed a sensitiveness to light, giving positive responses. At 



