392 PROCEEDINGS OF THE AMERICAN ACADEMY. 



certainty that Limax, like Helix, is unsuitable for use in experiments 

 where constancy in the character of the reactions is necessary. 



11. Cricket Frog {Acr is gryllus Le Conte). 



In the search for animals with the type of eye often known as the 

 " camera eye " which could be employed in these experiments, the 

 choice appeared to be rather limited. Of the vertebrates which could 

 be used out of water most appear to be either indifferent to the action 

 of directive light, or else their reactions are of such a complex nature 

 that the natural responses to light are inhibited by other external 

 stimuli or by fear. Certain of the amphibia appeared most promising, 

 especially the frog, this animal having been experimented upon by 

 .Graber ('84) more than twenty years ago, and by a number of observers 

 since that time. Two recent papers, one by Parker ( : 03^ ) and the 

 other by Torelle (:03), treat rather fully of the reactions of frogs to 

 light. Parker's observations relate exclusively to the leopard frog 

 {Plana pipiens Gmelin), while Torelle used this species and the green 

 frog {U. clamata Daudin) indiscriminately. 



In previous years, at Ann Arbor, Mich., I had incidentally noted the 

 marked positive phototropism of the little cricket frog, which is 

 abundant about ponds and lakes and in the marshes of that region. 

 It is an active little animal, capable of making leaps to a distance of a 

 meter or more. Specimens placed on a large table top above which 

 swung an electric light at a height of a half-meter or so were observed 

 to make long leaps toward the light. They usually missed striking the 

 globe, seldom going so high, and landed on the other side of the table 

 headed away from the light. Ordinarily they would remain in this 

 position for a short time, then turn around so as to face the light again, 

 and then, after another interval, again leap toward it ; this proceeding 

 would be repeated until a chance jump carried them completely off 

 the table on to the floor. The decisiveness and persistence of the re- 

 action suggested that this animal might prove even better to work with 

 than the common species of Rana. In consequence, through the kind- 

 ness of friends in Ann Arbor, several dozen specimens of Acris were 

 obtained from that place for the purpose of these experiments. In the 

 meantime a number of other amphibians, including two species of 

 Plethodon and Diemyctylus viridescens, were tested as to their light 

 r3actions, but although these in general appeared to be negative to 

 light, as would be suspected from their habits, their reactions to the 

 intensity of light used did not appear sufficiently marked to make 

 them suitable for these experiments. 



