REACTIONS OF AMBLYOPSIS TO LIGHT. 32 1 



of fishes in the dark than when the light strikes them from the 

 side. It is possible that with the light overhead, the brain and 

 spinal cord are affected directly on account of the transparency 

 of the tissue above them. 



For comparison, I caught a number of small specimens rang- 

 ing from 15 to 25 mm. in length, placed 10 of them in the 

 aquarium and made observations as I had done with the adults. 

 In these fishes, the eye was plainly visible as a small black spot 

 beneath the skin, while in the adults there is no external indica- 

 tion of an eye. With the light at the end of the aquarium and 

 the whole aquarium lighted, the thirty counts showed 1 1 5 fishes 

 in the end of greater and 185 in the end of lesser intensity, as 

 compared with 85 to 215 in the case of the adults. With the 

 left half dark there were 60 in the light to 240 in the dark, as 

 compared with 98 to 202 in the adults. With the right half 

 dark, 48 in the light to 252 in the dark, against 84 to 216 adults. 

 The light was then placed above the aquarium as before and 

 counts taken. When the left end was dark there were 28 fishes 

 in the light to 272 in the dark and with the right half dark there 

 were 25 in the light to 275 in the dark, as compared with 68 to 

 232 and 64 to 236 in the case of the adults. Here again we 

 have a larger percentage of fishes in the dark when the light is 

 above, and, further, these young fishes seem to be more sensitive 

 to the light than the adults. What is the reason for this ? 

 Thinking that the eye might play some part in this difference I 

 removed the eyes from 10 young. Seven of these recovered in 

 good condition. Of these I took five, all of which were about 

 an inch in length, and 52 hours after the operation made the first 

 observation. 



With the light at the end and the left half dark, thirty counts 

 gave me 19 fishes in the light to 131 in the dark, and with the 

 right half dark, 22 in the light to 128 in the dark, as compared 

 with 48 to 252 and 60 to 240 in the case of the young with eyes.' 

 These observations show that there is practically no difference in 

 the reactions of the young with eyes and those without eyes. 

 Hence the eyes play no part in the reaction. 



In making these experiments the counts often varied consider- 

 ably in the same series even though the external conditions, so 



