140 LESLIE B. AREY 



It (loos not seem probable that quantitative differences in the 

 degree of pigmentation can be the cause of such relations, for if 

 the relative amounts and the distribution of pigment in Fundulus 

 and Abramis be compared at 5°C. in the Ught (figs. 5, 1) and at 

 either temperature in the dark (figs. 7, 3) it must be admitted 

 that quantitative differences do not adequately explain the 

 conditions that exist. 



A clearer insight is gained if these responses are viewed from 

 the standpoint of cell organization. We can think of two gen- 

 eral types of pigment cells in which the pigment distribution is 

 correlated with the behavior outhned above. Thus, in one type, 

 the pigment would tend to remain at the distal end; such a 

 cell would show maximal expansion but relatively incomplete 

 contraction. In a second type of cell, in which the pigment 

 aggregates more proximally, maximal contraction but incom- 

 plete expansion would be accompHshed. Although other species 

 of fishes should be studied before a final conclusion is reached, 

 this set of relations may be general. The correlation can be 

 stated, at least tentatively, as follows — the highest degrees of 

 expansion and contraction in the retinal pigment of fishes are 

 mutually exclusive in the same retina. 



2. Frog {adult and larva) . As in many other lines of physiologi- 

 cal work, the frog has been used to a large extent by investigators 

 of retinal physiology. 



Ewald und Kiihne ('78) performed the first experiment in 

 which the position of the retinal pigment of the frog was shown 

 to be dependent upon temperature. According to their account, 

 after 2 hours' immersion in ice water in the dark, the pigment 

 showed a distribution similar to that obtained at 17°C., which 

 may be called a state of contraction.^ When, however, frogs 

 were subjected to 30°C. for 2 hours, an expansion occurred in 

 which lightly pigmented processes were said to extend even to 



^ This, however, does not coincide with an earlier statement ('77, p. 250) of 

 the same authors, "Vor allem ist die Temperatur von ausserordenlichem Ein- 

 flusse .... Frosche, welche 1-2 Stunden in Eiswasser gehalten wurden, 

 liefern schwarze Netzhiiute, indem das ganze Epithel mit ausschliipft, und 

 nicht viel besser verhalten sich die Priiparate von solchen, die bei 5°-10°C. im 

 Dunkeln verweilten." 



