130 LESLIE B. AREY 



dim li«2;lit. It is probable that this precaution was sufficient, for. 

 as will be shown later, the movements of the cones of Abramis, 

 the only fish worked upon, are not rapid and moreover no changes 

 occur even when the excised eyes, immersed in water, are sub- 

 jected to fight or to darkness. 



Temperature is an important factor that must be considered 

 in the adaption of cones. In anticipation of certain results 

 that will be found in another part of this paper, it may be said 

 that the cones of fishes are maximally extended at about 25°C. 

 in the dark (fig. 27), and in the case of Abramis at least, they are 

 also maximallj' shortened at 5°C. in the dark (fig. 25) . Moreover, 

 as temperature does not affect the length of the cones when they 

 are under the influence of light, the animals may be kept at 

 a temperature of 25°C. during an entire experiment and the re- 

 sulting movement of the cones will then be solely traceable to 

 conditions of fight or darkness. 



The results on the cones of Abramis may be summarized 

 as follows : 



Diffuse daylight 



15 minutes, cones much shortened — perhaps two thirds 



23 minutes, approximately the same condition as at 15 minutes 



30 minutes, shortening not quite complete in most animals 



45 minutes, maximal light adaption 

 Darkness 



13 minutes, cones somewhat extended — one third {'!) 



20 minutes, extension practically complete 



30 minutes, maximal dark adaption 



The adaption times of the cones of Abramis are longer than 

 those given by Stort for Leuciscus. This, in part, may be due 

 to the wider range between the positions of maximal light- and 

 dark-adaption which was produced by the aid of elevated 

 temperature. 



Englemann ('85), working on the frog, was the first to discover 

 that the movements of the cones were not accomplished in- 

 stantaneously, but required definite periods of time. He also 

 observed that elongation in the dark was a longer process than 

 shortening in the light. My results on Abramis do not entirely 

 support his latter view. At first the cones of this animal do 



