166 PROCEEDINGS OF THE AMERICAN ACADEMY. 



says they "usually conceal themselves under fallen leaves and among 

 the tangle of water weeds. On warm, sunny days in early spring, 

 however, they bask openly in the sunshine along the shore." Another 

 instance is given by B. Gr. Smith, (:07, p. 6), who remarks that " Cryp- 

 tobronchus comes forth but seldom in the daytime except during the 

 breeding season," and (p. 32) " with the close of the breeding season, 

 becomes more shy, avoids the light and is seldom seen in the open." 



Temperature. Torelle (=03, p. 475) stated that the positive photo- 

 tropism of the frog increased as the temperature was raised. If, how- 

 ever, the temperature rose above 30° C, these animals were indifferent 

 to light, and if it fell below 8° C, they became negative. Cole (07, 

 p. 401) has shown conclusively that conditions of temperature influ- 

 ence the photic responses in Rana. As has been stated, his method 

 was to place the animals between two lights of equal intensities but 

 different areas. When a frog has been cooled to from 6° to 10° C, it 

 went toward the smaller illuminated area, but after it became warm its 

 reactions were uniformly toward the larger area. 



Previous photic stimulation. Configliachi and Rusconi (:19) noticed 

 that after Proteus had been exposed to light for some time, its reac- 

 tiveness to that stimulus decreased. Reese (:06, p. 94), in experi- 

 menting with Cryptobranchus and Necturus, found that " the responses 

 to light were much more marked for the first ten or a dozen stimula- 

 tions." Torelle (:03, p. 47), on the other hand, observed that, after 

 five to eight hours' exposure to light, frogs exhibited the same positive 

 phototropism as before. 



Stereotropism. Eigenmann and Denny (:00, p. 34) in speaking of 

 Typhlotriton, say that " it seems probable that sterotropism rather than 

 negative heliotropism accounts for the presence of this species in caves. 

 Torelle (:03, p. 477) found that Rana was strongly stereotropic below 

 8° C. This stereotropism was associated with a change from positive 

 to negative phototropism, and, as Holmes (:06, p. 349) has pointed 

 out, may have been responsible for such change. 



Age, Banta and McAtee (:06, p. 71) in their experiments with the 

 cave salamander found that " all larvae are very much more responsive 

 to light stimulus than the adults, the young larvae more so than the 

 older." 



Surrounding medium. Torelle (=03, p. 473) has shown that frogs 

 will go toward the light under water as well as in air. The change in 

 surrounding medium, and from walking to swimming, apparently does 

 not alter the reactions. 



