XI THE COLOURS OF AMPHIBIANS 227 



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 Larv^ 



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 



