520 A. B. DAWSON 
the legs and at the bases of the gills. In the majority of animals, 
however, the yellow pigment, which is obscured by the black, 
becomes more apparent, and the black mottling, if present, is 
consequently emphasized. In the following discussion, when 
melanophores or pigment cells are spoken of, it is the black 
dermal chromatophore that is always referred to, unless other- 
wise stated. 
B. Effects of light and background 
1. In other Amphibia. Light has been shown to have an effect 
on the melanophores of various animals. Some of the earliest 
observations were made on Rana esculenta and Hylaarborea 
by von Wittich (’54), who found that in bright lights these 
animals were citron-yellow and in the dark, grass-green. His 
results were confirmed by Hering und Hoyer (’69), Dutartre 
(90), Steinach (’91), and many others. Flemming (’97 a, ’97 b) 
observed that larvae of Salamandra maculosa were light colored 
in bright light and dark when left in darkness. In general in 
the Amphibia bright illumination has been found to cause a 
contraction of the melanophores. 
Rogers (’06) noted in Diemyctylus viridescens that, if the 
temperature of the water were kept constant and the intensity 
of the light increased, the color of the animal became corre- 
spondingly lighter. Babak (710, 712, 713) found that axolotl 
larvae placed in the light were pale and those placed in darkness 
were dark. Hooker (12) states that, in general, the warmer, 
dryer, and more highly illuminated the frog (Rana fusca) is, 
the lighter in color it will become. Pernitsch (13) confirmed 
Babak’s observations on axolotl larvae. With the larvae of 
Amblystoma punctatum and opacum similar results have been 
obtained by Laurens (14, ’15, ’16), who found that animals 
kept in the light on an indifferent background are pale, while 
those kept in the dark are dark. But larvae placed in a bright 
light on a black background show a maximally expanded con- 
dition of all the melanophores. Furthermore, animals which had 
been kept in either darkness or light for a considerable time 
