REACTIONS OF AMPHIBIAN LARVAE TO LIGHT 205 



to light. But the reactions to light are very different according 

 as the larvae have been adapted to light or darkness. The nor- 

 mal larvae which have been kept in the dark, and are, therefore, 

 darkly pigmented are very much more sensitive than are those 

 which have been allowed to remain in the light. When darkly 

 pigmented larvae, which have been kept in the dark are compared 

 with darkly pigmented larvae which have been kept in the light 

 on a black background, it is seen that the latter are much less 

 sensitive to light, and show a smaller percentage of positive 

 responses, and a much larger percentage of indifferent reactions 

 and of no reactions. The pale larvae which have been kept in 

 the light on a white background are also much less sensitive to 

 light than the darkly pigmented ones which have been kept in 

 the dark, and are equally lacking in sensitiveness to those darkly 

 pigmented larvae which have been kept in the light on a black 

 background. 



The eyeless larvae show also that those which have been kept 

 in the dark are more sensitive to light, giving a larger percentage 

 of positive responses than those which have been kept in the 

 light. 



In both cases, then, it may be said that dark adaptation brings 

 about a condition of greater sensitiveness to light, irrespective of 

 the condition of the pigmentation in the skin. The retinal pig- 

 ment reacts to hght probably in the way that it usually does, 

 that is to say, when the animal is kept in the dark, the pigment 

 migrates proximally, and when the animal is kept in the light, 

 it migrates distally. In the dark-adapted animal then it might 

 be assumed that, since the pigment was contracted, the retinal 

 elements were more sensitive to light, and that the reverse might 

 be said of the animal kept in the light. The condition of the ret- 

 inal pigment probably does affect the sensitiveness of the normal 

 larvae, although, as we have seen, the skin pigment does not 

 have any influence on the sensitiveness of either the normal or 

 the bhnded larvae. It has been found that in some amphibians 

 there is a connection between the nerve terminations of the 

 eyes and those of the skin, as is to be inferred from results when 

 the skin is illuminated. Engelmann ('85) found that changes 



