Colour Variation in Vipera berus. 131 



{a) The Extent to Which Colour Variation is Found. 



The most casual observer of a representative collection 

 of British adders — a collection such as is to be seen in the 

 Zoological Museum at Edinburgh University — could hardly 

 fail to be at once struck with the fact that adders do differ in 

 a most remarkable manner in colour. But to exhibit this 

 range of variation to its full extent, the collection must be 

 representative in two senses. First, the specimens must have 

 been taken from widely differing localities ; and secondly, 

 they must have been taken over a period of at least three 

 seasons of the year — spring, summer, and autumn. Assum- 

 ing that we have before us a collection of adders, truly 

 representative in the above sense of the word, what variations 

 of colour do we find to be present ? 



A collection divides itself into two portions from the point 

 of view of colour; first, the adders that exhibit one colour 

 only, which we may term for convenience "whole-coloured"; 

 and secondly, adders which exhibit combinations of two or 

 more colours, this latter group including the great majority. 



Midti-Coloii^recl Adders. 



The vast majority of adders exhibit combinations of 

 colours, affecting different parts of the body in varying 

 degrees. As a rule, the characteristic specific markings are 

 of a much darker colour than the rest of the body, i.e., the 

 Y-shaped head marking and the zig-zag dorsal line are of 

 a black or dark brown colour, and show up more or less 

 conspicuously from the general body colour. The same 

 remark applies to the lateral line of spots. If we examine 

 more closely a series of ordinary adders, we find that it is 

 possible to assign certain colours to definite parts of the 

 body. 



In the region of the head there are found specimens with — 



Black and white lip scales. 

 Yellowish red lip scales. 

 White throat scales with black edges. 

 Yellow or reddish throat scales. 



