186 C. F. CURTIS RILEY 



photic stimuli was an electric light situated 50 cm. above a 

 flat surface on which the frogs were placed. A. gryllus faces 

 the source of illumination and leaps toward it. When a frog 

 jumps past the light, the animal remains with its back turned 

 toward it for a short time. Then it turns in such a manner 

 as to face the light and again leaps toward it. Cole (I.e., pp. 

 393-401) also found that both A. gryllus and Rana clamata 

 Daudin respond positively to light with an intensity of from 

 1.25-5 ca.m. by turning toward the source of illumination, but 

 that individuals of the latter species were much the slower in 

 their responses. He noticed that the positive response of A. 

 gryllus occurs more quickly and uniformly when light of 5-20 

 ca.m. is used. This is in accord with the present writer's ex- 

 periments on Bufo americanus as it is also in accord with the 

 results of Parker (I.e.) with Rana pipiens Schreber already 

 mentioned. It should be stated that during these experiments 

 of Cole with A. gryllus and R. clamata, the animals were con- 

 fined in glass boxes which were of such dimensions that the 

 amphibians could turn readily in any direction, but were unable 

 to jump away. My experiments are also essentially in agreement 

 with those of Mast (191 1, p. 219-220). This worker subjected 

 seven toads to light from a single source. Two intensities were 

 used, one of 12.5 ca.m. and the other of 25 ca.m. Five of these 

 toads were small ones, but the exact size is not given. The 

 following quotation presents the results which have more direct 

 bearing upon the experiments described in the present paper: 



"They all oriented directly- and fairly accurately. If placed on the 

 table in the beam of light so that one side faced the glower they turned 

 slowly but directly until they faced the light and then hopped or walked 

 toward its source, stopping frequently for a few moments at intervals 

 on the way. * * * The toads always went directly toward one or 

 the other of the two sources." 



IV. RESPONSE TO STRONG DIFFUSE DAYLIGHT 



It was found that young individuals of Bufo americanus 

 respond to diffuse daylight of relatively strong intensity, and 

 a number of experiments were performed in which light of this 

 nature was employed. The glass trough containing the toads 

 was placed on a table, having a black surface, at a distance 

 of 50 cm. from an east window. A glass plate, painted a dead 

 black on the under side, was placed over the top of the experi- 

 mentation dish. Then the strip of black paper, covering the 



