BEHAVIOR AND COLOR CHANGES OF TREE FROGS 67 



to confirm in the course of my studies. To certain of these 

 I shall have occasion to refer repeatedly in what is to follow. 



By way of introduction to this phase of my problem let it 

 be said that, while many points of difference will be found as 

 the two species are compared, I have been somewhat sur- 

 prised in noting the many features of agreement which have 

 come to light in their comparison. Hyla arbor ea shows the 

 same individuality of behavior as does H. versicolor; it also 

 exhibits the same erratic aspects of color reaction which have 

 already been passed in review. From Biedermann's account 

 I had confidently anticipated a degree of constancy in beha- 

 vior which has not been realized under actual experiment. 

 Let it be noted that my observations on this species have been 

 restricted to the laboratory. I have not studied it in nature. 

 Again, my work has been limited to a comparatively brief 

 period, and to a single season. Except for the previous work 

 with the former species I should feel less confidence in the re- 

 sults relating to the latter. 



Two rather primary objects prompted my experiments on 

 this species: First, a desire to compare its behavior with that 

 of H. versicolor; and second, a review of the experiments and 

 conclusions of Biedermann. As a preliminary to the latter it- 

 may be well to briefly summarize some of the more funda- 

 mental of his methods and results, but only in so far as they 

 pertain to color changes. Furthermore, I shall not concern 

 myself with the elaborate chemical details which occupy a large 

 place in his investigations. 



It has long been held, following the experiments of Lister 

 ('58), that the nervous system was directly involved in these 

 color changes, and further that they were under control of the 

 animal, and operative only through the sense of sight. This 

 view is held also by Boulenger ('97), who says, " That these 

 rapid color changes harmonize, within certain limits, with the 

 surroundings, is well known. The researches of Dutartre on 

 Rana esculenta have shown that the changes are controlled 

 by the animal, the contraction and expansion of the chroma - 

 tophores not being due entirely to the direct action of light 

 and moisture upon the skin, but also to a reflex action of the 

 sympathetic nervous system brought about by the visual im- 

 pression. Comparative experiments conducted on frogs possessed 



