198 



HENRY LAURENS 



epidermal pigment cells do not show sufficient regularity of re- 

 sponse to light and darkness to fall in line with those of the corial 

 melanophores. The xanthopores seem always to remain ex- 

 panded. 



RESULTS 



The state of the melanophores of normal and eyeless larvae 

 of A. tigrinum under different conditions are in complete agree- 

 ment with those of A. punctatum and A. opacum. If normal 

 seeing larvae are placed in bright diffuse light over an indiffer- 

 ent background and in darkness, and kept there, it will be seen 

 after several days, that the melanophores of the animals kept in 

 the light are partially contracted (| to j expansion) (fig. 5), 

 while those of the animals kept in darkness are partially expanded 

 (f to I expansion) (fig. 6). Eyeless larvae show the reversed 

 condition, the melanophores of those in the light being expanded, 

 of those in darkness, contracted. Table 1, which is reproduced 

 from my earlier paper ('15), summarizes these observations, the 

 conditions of the melanophores over a white and a black back- 

 ground being also included. 



TABLE 1 

 State of the melanophores after long continued illumination and darkness 



But the reactions, or primary responses, to light and dark- 

 ness of the melanophores of the normal larvae are different 

 (table 2), and do not agree with the conditions of the melano- 

 phores, which have just been described. 



When the melanophores of larvae, normal and eyeless, that 

 have been in darkness for only a few hours, are examined, it is 

 seen that they are completely contracted, appearing as fine 

 black dots. If these larvae, over an indifferent bottom, are now 

 exposed to bright diffuse light the melanophores soon (five min- 



