128 LESLIE B. AREY 



condition of distal acciunulation requires additional time after 

 the 'front rank' of pigment granules has arrived at the position 

 of maximal extension. In the determinations made by me, 

 light adaption was not considered to be completed until the 

 pigment was thus maximally expanded. 



The results obtained on the retinal pigment of fishes were 

 as follows: 



Aineiunis 



Diffuse daylight 



30 minutes, pigment incompletely extended 



40 minutes, pigment fully extended, but homogeneously distributed 

 1 hour, maximal expansion 

 Darkness 



45 minutes, pigment about half contracted 

 1 hour, maximal contraction 



The movements of Abramis were more rapid, notwithstand- 

 ing an apparently heavier pigmentation of the retina. 



Abramis 



Diffuse daylight 



15 minutes, lightly pigmented processes three quarters extended. Most of 



the pigment at the bases of the cells 



30 minutes, processes fully extended. Distal pigment accumulation 

 begun 



45 minutes, maximal expansion 

 Darkness 



20 minutes, pigment about half contracted 



30 minutes, maximal pigment contraction 



The results of the dark adaption on Fundulus were less satis- 

 factory, since the delimitation of the pigment in darkness is 

 poorly defined. 



Fundulus 



Diffuse daylight 



45 minutes, pigment fully extended; but little tendency exhibited towards 



distal accumulation 

 1 hour, maximal expansion 

 Darkness 



45 minutes to 1 hour, maximal contraction 



As regards the adaption time in the frog, Stort ('87) beheved 

 that in 1 hour of bright, diffuse daylight or in 4 hours of dark- 



