258 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
them. But when eyeless toads were tested (p. 191), they were equally 
positively phototropiec 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 
(L), 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. 
