MOVEMENTS IN THE VISUAL CELLS 165 



WTien the rods and cones of Ameiurus and the cones only of 

 Abramis and Fundulus were tested, the following results were 

 obtained. The rods of Ameiurus moved both in light and in 

 darkness, whereas the cones were stimulated only by light, no 

 elongation occurring in the dark even when the experiment 

 continued for 4 hours. The cones of Abramis and Fundulus 

 did not change their positions to any extent either in hght or 

 in darkness. In the light the cones of Abramis, which were more 

 carefully investigated than those of Fundulus, at most showed 

 only slight retraction and never closely approached the exter- 

 nal hmiting membrane. If light did exert a direct influence 

 on the cones or retinal pigment of this fish, the changes would 

 be extremely easy to distinguish due to the wide difference 

 between the light- and dark-adapted phases. 



Since neither the cone cells nor retinal pigment of Abramis 

 underwent movements under these conditions, it is possible 

 that the accumulation of catabolic products, occasioned by the 

 interruption of the blood supply, was responsible. Experimenta- 

 tion of the following kind shows the importance of maintaining 

 the vascular circulation. If the optic nerve only of Abramis is 

 cut, the retinal elements undergo their normal movements in 

 darkness and in light. If, however, all the blood vessels and 

 muscles are cut and the eye ball is attached to the body by the 

 optic nerve only, no movements result. The objection may be 

 made that some nervous mechanism is deranged by cutting 

 these muscles and blood vessels, but this is hardly probable, 

 as further experimentation, to be presented in a subsequent 

 paper, on this and other fishes has shown. 



In cases Uke the movements of the pigment or cones in excised 

 eyes of Ameiurus through the action of light only, it is probable 

 that an inhibitory tendency is also present, but the response to 

 the stimulus furnished by light is sufficiently vigorous to over- 

 come it. Either a less vigorous stimulus or response may ex- 

 plain why no movements of the cones and pigment occur in 

 darkness. 



An inhibition due to the presence of unremoved catabolic 

 products, as postulated here, would be merely a form of auto- 



