XI 
THE COLOURS OF AMPHIBIANS 
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portant as compared with the contractile pigment 
cells of the dermis. The colour-changes are due to 
variations in the degree of contraction and expan¬ 
sion of these pigment cells, or of their protoplasmic 
contents. 
The pigments, where they have been investigated, 
have been found, as in the case of fishes, to be either 
lipochromes or melanins. Guanin is also present in 
the skins of Amphibians, but the amount is smaller 
than in fish, and the effect on coloration much less 
obvious. The lipochromes and melanins, occurring 
separately or combined, produce such colours as 
black, brown, yellow, orange, and so forth, while in 
association with optical effects they produce such 
colours as blue and green. The skin of the frog 
when steeped in alcohol loses its green colour owing 
to the fact that the lipochrome dissolves out. It is, 
however, an old observation that the colour will 
return if the grayish skin be covered over with wet 
yellow tissue paper (Krukenberg). 
The Colours of the Larvae 
The Amphibia display in general a very marked 
metamorphosis during the course of development, 
and there are often notable differences in the colour 
of the larval and adult stages. The larvae are 
peculiarly susceptible to environmental influences 
as regards colour, but they differ from the adults in 
apparently being more sensitive to heat than to light, 
and also in the relative stability and permanence of 
the effect produced. There is some evidence to show 
that the elements producing coloration are more 
