232 
COLOUR IN NATURE 
CHAP. 
hardly be regarded as of excretory nature, they 
apparently tend to decrease during the process of 
development, but, on the other hand, they are 
abundant in adults showing specialised colouring, as 
in the case of the spotted salamander, and often 
increase in amount during the breeding season in 
individuals which exhibit a seasonal change. Reinke 
(Arch, f mikrosk. Anat. Bd. 43, 1894) has sought 
to solve some of those difficulties, and especially the 
disappearance of the yellow cells from the peritoneum, 
by the supposition that the yellow pigment may be 
converted into the black. This is strongly opposed 
by Fischel, and the question apparently does not at 
present admit of decisive settlement. It thus seems 
that the simultaneous existence of both black and 
yellow pigments prevents us here, as in so many cases, 
from accepting in its entirety the theory that pigment¬ 
ation is the result of an excretory process. 
Although our present knowledge does not enable 
us to make any statement as to the origin of the 
lipochromes in Amphibia, yet the developments 
described above disclose some interesting facts in 
connection with their distribution. The statements 
of Fischel and Bedriaga taken together show clearly 
that in the early stages of development the two sets 
of pigments are closely intermixed, and that the 
growth of the larvae or the transition from larval to 
adult life, tends to be accompanied by a process of 
segregation, the yellow pigments accumulating at 
certain spots and the black at others. The process 
is an interesting one because it seems to occur 
frequently in birds, in the males as compared with 
the females. Its external result is to greatly increase 
