258 bulletin: museum of comparative zoology. 



them. But when eyeless toads were tested (p. 191), they were equally 

 positively phototropic in all the lights used. To quote (p. 206), 

 " it may be said that, while both the skin and eyes are sensitive to 

 the whole range of the visible spectrum, color-sensitiveness is present 

 only in the latter." 



The results thus summarized seem to point, therefore, to the view 

 that the blue end of the spectrum is the most effective in the produc- 

 tion of phototropic responses, and that this is true for both positively 

 and negatively phototropic forms. The results obtained by Graber 

 on the toad, and by Dubois on Proteus, do not agree with this. But 

 there is no certainty that any of the results obtained by the earlier 

 investigators in this subject are due unquestionably to a response to 

 difference in color; or wave lengths, as such, rather than to the differ- 

 ence in intensity, or to the radiant energy content, of the several lights. 



The experiments described in the present paper were carried out (1) 

 to ascertain whether amphibians showed a sensitiveness to lights of 

 different wave lengths, exclusive of their intensity value; and (2) 

 to decide whether this sensitiveness, if present, resided in the eye, 

 in the skin, or in both the eye and the skin. 



It is a pleasure to acknowledge my gratitude to Prof. G. H. Parker, 

 under whose direction the work was undertaken, and without whose 

 untiring interest, suggestions, and criticism it would not have been 

 accomplished. I take this opportunity also to express my thanks to 

 Mr. A. O. Gross, a student in the Laboratory, for invaluable assistance 

 in the construction of some of the details of the apparatus. 



II. Methods. 



1. Apparatus. 



The apparatus used in these experiments is based on appliances 

 worked out by G. H. Parker and E. C. Day, an account of which is 

 shortly to be published. The plan of the apparatus is shown in Figure 

 1. It consisted of two light-generators, A and B, so placed, with 

 reference to each other, that the light from A entered a dark chamber 

 (Z), opposite that from B; and of a table (7"), covered with a slab 

 of slate, on which the animals whose reactions were to be tested were 

 placed. 



