120 BRITISH SERPENTS. 
who has observed many adders in nature will agree in 
this general statement, that old adders are much 
duller in colour than young ones—the young males 
being the brightest of all, the old females the dullest 
of all, in colouring. Adders of the same age and sea: 
in the same locality might be very nearly identical ; 
but adders of different ages and seaes, thoneh from 
the same locality, will be found to exhibit great varia- 
tion. Thus age in connection with sex must be con- 
sidered the two main factors in the production of the 
varying colours of adders. Locality would seem to 
have but httle influence. 
The old female adder shown is a good example of 
what was just mentioned—viz., the disappearance of 
the dark markings with great age. She measured 263 
inches in length, so there was no doubt as to her 
maturity, and the zigzag line is discernible only for 
an inch or two a short distance behind the neck. 
The young male is the smallest adder I have taken 
in the Monnow Valley, being 193 inches—equal proof 
of his youth in that locality, where the average length 
of males is two feet. 
All these considerations might apply to other 
animals, but in the case of reptiles there is another 
point to take note of, and that is sloughing. Has 
casting the slough any effect on the colour variation ? 
Strictly speaking, I think not. That is, the colours are 
not diferent after sloughing, but they are better seen. 
(The smooth snake is not here referred to.) The 
