THE ADDER. .111 



Colours found. — Note first the actual colours that 

 are found to be present in adders. These will be 

 found to fall under two heads : first, colours descrip- 

 tive of the general appearance of the adder ; second, 

 colours that are found only on particular parts of 

 the body. Amongst the first I find all the follow- 

 ing terms used by correspondents to describe the 

 general appearance of adders: black, dark - brown, 

 olive - green, warm - brown, coppery - red, dirty pink, 

 brownish-grey, pallid -grey, grey, and almost white. 

 All these terms are correct descriptions of the speci- 

 mens referred to, so that it may be said literally that 

 adders vary from black to white. But these terms 

 do not refer to the markings, which are generally 

 described as being black, brown, or mahogany-red. 

 In addition to these colours the following may be 

 seen in one or other part of the body : yellow, 

 orange, deep-blue, mottled grey, and pale-blue. The 

 question to be considered is, What determines the 

 presence or absence of any of these colours or com- 

 binations of them in any given specimen ? 



In this connection the small red viper will be 

 dealt with separately, as it is fairly constant in 

 colour, and does not exhibit the variation of the 

 ordinary adder. 



Factors concerned. — Bearing in mind the exact 

 question at issue, the factors concerned in the pro- 

 duction of colour variation in adders will probably be 

 found to fall under one or other of the following : — 



