130 PTOceedings of the Eoyal Physical Society. 



X. Colour Variation in Yipera berus {the Common Adder) — 

 («) Its Extent ; (h) Its Significance and Explanation. 

 By Gerald Leighton, M.D., F.R S.E. [Plate III] 



(Read 26th January 1903.) 



Introductory. — The scientific student who sets out to learn 

 something of the life-history of serpents cannot fail to be 

 struck with the fact that almost all the authoritative work 

 that has been done on the order Ophidia has reference to 

 only one aspect of an organism, namely, the morphological 

 aspect. It is, perhaps, well that ophidian morphology should 

 have been thoroughly dealt with first, since a correct 

 scientific classification is based on morphological charac- 

 teristics alone, to the neglect of the physiological processes ; 

 but the former investigations having been carried to a high 

 state of perfection, it is surely high time that the ophiologist 

 turned his attention to the physiological side of these 

 interesting reptiles. True, there is one portion of serpent 

 physiology which has had much labour spent upon it, and 

 that is the problem of the determination of the composition 

 of snake venom, and the search for an effective antidote, a 

 twofold investigation which promises to supply material for 

 still much more research in the future. But apart from the 

 question of the secretion of venom and its action, very little, 

 at any rate as far as British species are concerned, has been 

 done to throw light on ophidian physiology, so that it may 

 not be uninteresting to draw attention to one of the 

 physiological problems in a British serpent, viz., the question 

 of Colour Variation. For our present purpose I shall confine 

 myself to dealing with one species only — so regarded at least 

 by those responsible for the existing classification — that 

 species being Vipera herus, the Adder or Viper, the sole 

 venomous reptile of Great Britain, and the only serpent 

 indigenous to Scotland (except the harmless Tropidonotus 

 natrix, which occasionally occurs in Roxburgh and Ber- 

 wick). 



