186 LESLIE M. AREY 



10. Ill excised eyes of \\w four fishes studied, light causes 

 a migration of the retinal pigment in Ameiurus only, whereas 

 the pigment of none of the fishes moves in darkness. The rods 

 of excised eyes of Ameiurus undergo movements both in the 

 light and in the dark, the cones move in the light only. Neither 

 exposure to darkness nor to light produces positional changes 

 in the cone cells of excised eyes of Abramis orFundulus. Where 

 tested, temperature was found to cause movements in the retinal 

 pigment and cone cells in the excised eyes of fishes. 



11. It is probable that the absence of responses in the excised 

 eyes of fishes is due to an autoanaesthetization caused by the 

 accumulation of catabolic products. 



12. Dittler's theory of the chemical stimulation of the cone 

 myoid, propounded to explain the movements of the cone cells 

 in isolated frog's retinas, does not satisfactorily meet many 

 conditions found in the responses of the cones of fishes. 



13. The effects of temperature upon the rods, cones, and retinal 

 pigment of the excised eyes of fishes are identical with those 

 found in living animals, hence it is probable that temperature 

 has a direct action upon these elements, its effect being physical 

 in the sense that the chemical activity of the protoplasm is 

 thereby accelerated to varying degrees. 



14. Temperature has no effect upon the retinal pigment of 

 the excised eye of the frog, therefore it is plausible that the 

 action of temperature in living animals is physiological, whereby 

 any adequate stimulus acting through the central nervous sys- 

 tem can produce a striking pigment expansion according to the 

 principle of specific energies. As in living animals the cone cell 

 of the excised frog's eye responds by a shortening at an elevated 

 temperature only ; it is probable that temperature acts directly 

 upon the cone myoid, for this response, unlike that of the pig- 

 ment, can not be interpreted by the principle of specific energies. 



15. Neither in the frog nor in Ameiurus are movements of 

 the retinal elements evoked by exposure of the skin only to 

 light. Hence the existence of an interrelation between dermal 

 photosensitivity and the responses of the retinal elements by 



