202 
ZOOLOGY: A. C. REDFIELD 
observing the initial and the later phases of phosphorescence there would 
be an actual discontinuity between the processes referred to above and 
those in the curves for the phosphorescence of slow decay. 
Summary. — (1) The regions of selective excitation (the bands of 
excitation) for the Lenard and Klatt sulphides are shown to coincide 
in position and extent with absorption bands in the transmission spec- 
trum of the substances. 
(2) The spectrum of the phosphorescent light during the first few 
thousandths of a second after the close of excitation, contains one or 
more groups of over-lapping bands the crests of each group forming a 
spectral series having a constant frequency interval. 
(3) The decay of phosphorescence during the first three hundredths 
of a second after the close of excitation may be described as consisting 
of two processes each showing a linear relation between I~' and time. 
The first and more rapid process lasts for less than 0.01 second for the 
three sulphides studied under the intensity of excitation employed. The 
second process probably persists for 0.06 seconds or more. 
(4) The phosphorescence of long duration of the sulphides under 
consideration is probably due to another group of bands of comparatively 
feeble initial brightness which come under observation only after the 
phosphorescence of short duration has vanished. 
1 The investigation was carried out in part with apparatus purchased by aid of a grant 
from the Carnegie Institution of Washington. 
2 Lenard and Klatt, Ann. Physik, Leipzig, (Ser. 4), 15, 1904, (225). 
Lenard, Ibid., 31, 1910, (641). 
* Becquerel, E., La Lnmiere, Vol. 1, 1861. 
5 Nichols, Philadelphia, Proc. Amer. Phil. Soc, 55, 1916, (494). 
6 Henri, V., Physik. Zs., Leipzig, 14, 1913, (516). 
7 Howe, Physical Rev., Ithaca, (Ser. 2), 8, 1916, (637). 
^ Nichols and Merritt, Washington, Carnegie Inst., Pub., No. 152, (84). 
9 Nichols, these Proceedings, 2, 1916, (328). 
THE REACTIONS OF THE MELANOPHORES OF THE HORNED 
TOAD 
By Alfred C. Redfield 
ZOOLOGICAL LABORATORY OF THE MUSEUM OF COMPARATIVE ZOOLOGY. HARVARD COLLEGE* 
Communicated by G. H. Parker, February 3, 1917 
The reactions of the melanophores of the horned toad Phrynosoma 
cornutum are of three distinct types: (1) Those which manifest them- 
selves in a daily rhythm of reactions, correlated with definitely changing 
* Contributions from the Zoological Laboratory of the Museum of Comparative Zoology 
at Harvard College, No. 292. 
