398 



PROCEEDINGS OF THE AMEllICAN ACADEMY. 



having the skin of the other specimen slipped over it, not responding 

 within two minutes in more than half of the trials, so that it had to be 

 started by mechanical stimulation. As a check experiment, the 

 enveloping skin was now drawn forward so that it covered the eyes as 

 well as the rest of the body. The frog no longer turned toward the 

 large light, but, on the contrary, an unexpected result was obtained ; 

 for it now turned in nearly all cases toward the smaller light, when it 



TABLE X. 

 Reactions of Acrts after the Optic Nerves had been cut. 



would have been expected to be indifferent, since both skin and eyes 

 were protected from the light. A larger series of experiments might 

 have explained this apparent anomaly,^ but by this time the specimen 

 had become exceedingly sluggish and inactive, and it was believed that 

 the results obtained sufficiently demonstrated that Acris discriminated 

 between the two areas by means of the light from them that entered 

 the eyes. 



It now remained to test animals by exposing their skin to the full 



8 Two pos.sible explanations of what may have caused the results obtained 

 suggest themselves : (1) The portion of skin covering the eye toward the small 

 light may have been more pervious to light than that over the other eye, due to 

 its having been stretched more tiglitly, to a difference in pigmentation, or 

 possibly to injury, such as an abrasion or a small perforation; or (2) it maj"^ be 

 that the light from a small area such as was used may have a greater penetrating 

 power through a membrane of this character tlian the more diffuse liglit from a 

 larger area. 



