400 PEOCEEDINGS OF THE AMERICAN ACADEMY. 



light alone. The results of this test are recorded in the right half of 

 Table X. It will be seen that each individual gave a preponderance 

 of reactions toward the light, except No. 3, which turned once in each 

 direction, and twice went ahead without turning. Three of the frogs 

 were thus undoubtedly positively phototropic to light stimuli received 

 by the skin, and the inherent inactiveness of No. 3 has already been re- 

 marked. From the totals it is seen that out of 44 trials 26, or more 

 than half, were positive, or toward the light, 5 negative and 13 

 indifferent. 



From the foregoing experiments it seems that the following con- 

 clusions may legitimately be drawn : 



1. Acris gryllm is preponderatingly positively phototropic, though 

 there is some inconstancy in the reactions of the same and of 

 different individuals, depending upon unascertained factors. 



2. Exposed to luminous areas of different size but equal intensity, 

 it turns in by far the greater number of trials toward the larger of the 

 two areas. 



3. The result is substantially the same when the skin of the 

 animal is protected from the light, but the eyes are exposed. 



4. Acris deprived of sight by severing the optic nerves, but having 

 the skin exposed to the light, is indifferent to the size of the luminous 

 field. 



5. From this it follows that the discriminating power as to the dif- 

 ferent areas lies in the eyes, and is the result, it is safe to infer, of 

 the ability of these organs to form comparatively clear images of 

 external objects. 



6. Acris with the optic nerve severed is still positively phototropic, 

 but in this case, where the light must be perceived by the skin, its 

 condition as regards image-formation and the consequent ability to 

 discriminate between luminous areas of different sizes is directly 

 comparable to that of an eyeless animal, such as the earthworm. 



12. Green Frog {Rana clamata Daudin). 



A number of experiments of a similar nature to those last described 

 were made with the green frog for the purpose of comparing its reac- 

 tions with those of Acris. The general method employed was the 

 same, but differed slightly in details. The frogs were placed beneath 

 a glass box 10 cm. X 12.5 cm. X 10 cm. high, and an attempt was made 

 to get them to orient in the normal position by means of the incandes- 

 cent lamp, as was done with Acris. They were so slow in respond- 

 ing, however, that it was found more expedient to raise the box and 



