202 HENRY LAURENS 



of the melanophores (see von Frisch, '11, and Babak '13). 

 This is supported by observations on the number of melano- 

 phores in seeing larvae that have been kept permanently in 

 light over white bottoms where the pigment cells are always 

 contracted. That the expanded condition is ineffective in this 

 regard is not claimed, for comparisons between larvae kept in the 

 light over white bottoms and those kept over black bottoms 

 show that the number in the latter is greater. 



In seeing larvae that have been kept in the light over indif- 

 ferently colored bottoms for some time the melanophores also 

 secondarily react. Continual or constant illumination does not 

 seem to be necessary for this secondary reaction. Comparative 

 observations have been made on larvae placed over an indiffer- 

 ent bottom in bright diffuse daylight, on those that have been 

 continuously illuminated in a dark room by an electric lamp 

 placed above the dish, the light being passed through ground 

 glass and thus diffused, and on those continuously illuminated 

 by light from a nitrogen-filled Mazda lamp passed through 

 'daylite' glass. All show after a few days the melanophores, 

 which expand at first when they are illuminated, to be con- 

 tracted (fig. 5). This, as was before found for A. punctatum, 

 is not a complete contraction, but what has been called a | to 



1 expansion. Ii takes, on the average, four days to come about. 

 In a few individuals it sometimes takes a shorter time, in some 

 it takes much longer, and in a few it never takes place. Table 



2 summarizes all of these reactions of the melanophores. 

 Normal seeing larvae of Amblystoma tigrinum kept in an 



aquarium with Elodea and other plants are when young a pale, 

 dirty, greenish gray which as the larvae grow older becofnes a 

 rich brown color. Eyeless larvae, on the other hand, are much 

 paler in general appearance, having been described as 'anemic 

 looking' by some who have observed my animals. In such an 

 environment as has been described the general background is a 

 black or dark one, and it is to this that the rich dark brown 

 appearance of the normal larvae is due. It is dependent upon 

 the eyes as is shown by the pale appearance . of the eyeless 

 individuals. 



