290 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



of balsam and lampblack, and, after allowing the animal to swim in a 

 brightly illuminated dish for several hours, it was killed, and both its 

 eyes prepared and examined. 



The two sets of experiments yielded essentially the same results, 

 namely, the eyes exposed to the light always presented the condition 

 normal for the light, and those kept in the dark always showed an ap- 

 proach, more or less incomplete, to the condition characteristic for the 

 dark. This incompleteness might be taken as evidence of a partial 

 sympathetic relation between the two retinas ; but I believe it is to be 

 explained otherwise. In both sets of experiments the eyes supposed to 

 be blinded were in reality only partially cut off from the light. In the 

 experiment with the light-proof box, I know by actual observation that 

 more or less light made its way through the optic stalk that projected out- 

 ward to the exterior, and thus gained access to the interior of the box. 

 If this is true of the experiment with the box, it is very probable that in 

 the second experiment light passed up through the base of the blinded 

 stalk, and thus reached at least the proximal part of the retina. 



These experiments, then, are not wholly conclusive, but, so far as 

 they go, indicate considerable independence in the relations of the 

 two optic stalks. For reasons to be given later, in connection with the 

 experiments on excised stalks, I believe I am justified in concluding that 

 the two retinas are, in reality, wholly independent of each other. 



Localized Photomechanical Changes. 



Another question that natui'ally presents itself is, whether different 

 parts of the same retina are sympathetic toward one another, or whether 

 they are entirely independent, i. e. whether or not a retina responds 

 locally to stimulus. 



To test this matter, I put minute drops of the mixture of balsam and 

 lampblack on the corneal cuticula of the eyes of several shrimps, and 

 let them swim for a few hours in well illuminated basins. On examin- 

 ing sections of their eyes later, it was found that under each mass of 

 applied pigment the retinal cells showed a condition characteristic for the 

 dark. This was most pronounced in the distal retinular cells, but was 

 also observable in the proximal retinular cells, as well as in the acces- 

 sory pigment cells. This experiment shows beyond a doubt that the 

 elements of the retina act locally, and respond to differences of light 

 and dark independently of one another. This independence furthermore 

 explains what is not infrequently seen in sections of otherwise normal 



