56 THE ZOOLOGIST. 



traces of their usual darker markings in a glow of vivid green (as 

 has been supposed), frequently tend to embellish and render 

 conspicuous these designs, notably the brown dorsal stripe.* 

 This is often transformed into an object of great beauty, and a 

 considerable amount of variety is displayed even in the arrange- 

 ment of this single feature. In many cases a broad band of 

 white runs down the middle of it, in others two thin white bands 

 accompany it on each side, the vertebral zone itself being 

 narrowed and darkened at the same time. Sometimes to the 

 last figure a delicate row of white specks is also added along the 

 centre of the back, which then displays three parallel white lines; 

 or again, the ocelli on the lateral portions each exhibit a white 

 centre. An exactly similar development of patterns takes place 

 with some forms of L. muralis, while the analogy with L. viridis 

 bilineata (or respectively trilineata and quinque-vittata) is evident.! 



The Sand Lizard offers other varieties interesting from this 

 point of view, such as one which may be called analogous to the 

 var. nigriventris of Lacerta muralis — a nigriventris form of L. 

 oxycephala has also been described — another is transversely 

 barred with black markings, like several forms of L. viridis and 

 L. muralis. 



Even the Blind-worm, Anguisfragilis, within its stringently 

 limited province of variation, furnishes varieties analogous to the 

 single- or double-lined, as well as to the speckled or cross-striped 

 forms of L. agilis above referred to, and if we look still further 

 to the Colubrine Snakes, we encounter numberless instances of 

 one species presenting simultaneously uniformly-coloured, spotted, 

 longitudinally or transversely striated varieties. 



* The difference between two males thus diversely decorated is very 

 striking : — later in the season they again resemble each other (having doffed 

 their ornamental costume), and generally assume a bluish-grey tint, owing, 

 I presume, to the "diminished vigour of the constitution." 



-| It is difficult to imagine why certain colour-varieties of one species 

 should occur often promiscuously amongst others, and elsewhere as fixed local 

 forms. In the latter case they are sometimes seen to gain the advantages of 

 adaptation to the environment at the same time. The particular two-lined 

 variety of L. viridis above alluded to has probably not become established in 

 more parts of Western Europe because it is here mostly confined to the 

 female, and in such cases of sexual dimorphism the preponderance of the 

 male element will generally prevent the young from acquiring, otherwise 

 than temporarily, characters peculiar to the female. 



