THE ADDER. 95 



• 



is 35 to 40 in males, 28 to 35 in females." 1 In 

 my own collection I find, as a rule, in the males 38, 

 39, or 40 pairs of sub-caudals, and in the females 

 very frequently 32 pairs. In the same way the 

 ventral shields vary. In males they are usually from 

 140 to 144 in number, in females from 144 to 150; 

 but these figures do not represent the limit of vari- 

 ation in either direction. 



Colouration. — By far the easiest manner of deter- 

 mining the sex of adders is by the colours in any 

 given specimen. Adders which exhibit a black or 

 dark-blue belly are males, and along with this is 

 often seen a striking contrast of very black markings 

 on a grey or yellowish background. The brownish- 

 green or olive colour with brown markings is char- 

 acteristic of females, this sex having a tendency to 

 shades rather than distinct colours. Reddish adders 

 with brown markings are also females. The throat 

 is often a sure test of sex. Adders which have the 

 throat scales black or edged with black are males, 

 those with reddish or yellow scales are females. 



Bearing in mind the shape and length of the tail, 

 and the more striking colouring of the male sex. 

 there is no difficulty in determining the sex of any 

 adder that comes under notice. Several of the 

 illustrations in this book show these sexual dif- 

 ferences. 



1 Boulenger, Zoologist, March 1892. 



