138 Proceediiigs of the Royal Physical Society. 



whole litter, consisting of fourteen young ones. The mother 

 was 26 J inches long, therefore obviously old; the young, as 

 I say, were just at full time. Of the fourteen young ones, 

 ten were males and four were females, but at that stage of 

 development there was no appreciable difference of colour- 

 ing, at any rate as far as the markings were concerned. All 

 the characteristic adder markings were quite distinct, but of 

 the same colour in the two sexes. Six months later, in 

 the early spring of 1901, I took several pairs of adders in 

 the act of copulation, and the two sexes were very sharply 

 defined by the colours noted above. The result of this series 

 of observations I found to be this. The young male of 18 

 to 20 inches in length, in the prime of life that is, was 

 found to be the most brilliantly coloured of all adders, black 

 and grey being at that time most sharply defined as distinct 

 colours. The young female of 20 to 22 inches was likewise 

 found to be the most brilliant of the females, the green and 

 brown and red being more sharply defined than either 

 before or later. In very old specimens of both sexes the 

 colours tend to lose their sharpness and become dull, this 

 being more noticeable in the females than in the males. In 

 very old females the markings tend to become obliterated 

 in the general body colour, not from an extension of the 

 pigmentation of the markings into the surrounding skin, but 

 rather, I think, probably from a cessation of the physio- 

 logical process of pigment production. Colour variation in 

 adders, then, is to be regarded as significant of Age as well 

 as Seo:. 



My own observations up to the present as to the produc- 

 tion of whole-coloured adders, i.e., black adders or greenish 

 adders, make me inclined to doubt Boulenger's explanation 

 of the process differing in the two sexes. It is doubtless 

 true that in some instances the dorsal dark line, instead of 

 being zig-zag, is represented by a continuous band formed by 

 the coalescing of the lozenge-shaped spots. But when this 

 happens, the dorsal line is simply a longitudinal black 

 band, not extending, so far as I have seen, laterally. 

 Similarly, the lateral line of spots may become joined 

 together as a longitudinal lateral line, but I have not 



