THE ADDER. 95 
is 45 to 40 in males, 28 to 35 in females.”! In 
my own collection IT find, as a rule, in the males 38, 
09, or 40 pairs of sub-caudals, and in the females 
very frequently 52 pairs. In the same way the 
ventral shields vary. In males they are usually frome 
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 
viven 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 havine 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 leneth 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. 
! Boulenger, Zoologist, March 1592. 
