IV LEYDIG ON THE EFFECT OF MOISTURE 137 



the sea coast may be caused by the greater moisture of the 

 atmosphere, notwithstanding the lowness of level, is supported 

 by a remark of Leydig's ^ on Helix nemoralis. Ley dig says : — 

 " The influence of light and warmth is very distinctly 

 evident in the colouring of Helix nemoralis in this region. The 

 fine citron yellow exhibited by the shell of this snail at 

 Mainz and in the sunny vineyards of the Main valley is 

 wanting^ on the banks of the lower Ehine. ... On the other 

 hand, it is interesting to notice how in the neighbourhood of 

 Bonn and lower down the Ehine the red of this snail deepens 

 into chocolate brown, and thus forms the beautiful variety 

 above mentioned, which must attract the attention of every 

 collector. It is perhaps too much to say that the moisture of 

 the plain of the lower Ehine determines this change of colour, 

 but we must keep in view the possibility that the moisture 

 coming up the valley from the sea, which certainly here at 

 Bonn has a distinct effect on the vegetation, has something to 

 do with the matter. . . . And just as in a former publica- 

 tion I attributed to similar causes the formation of black 

 varieties of our native reptiles, such as Vipera berus var. 

 prester, Lacerta vivipara var. nigra, the black variety of 

 Anguis fragilis, so I would maintain that there is a connec- 

 tion between the origin of the black varieties of Lacerta 

 muralis which have meanwhile been made known by 

 Eimer . . . and be it noted all of them occurring on the 

 small islands of the Mediterranean, and the action of the 

 moist sea air."- Leydig goes on to mention that in the 

 Entomologische Zeitung of Stettin, in 1877, a collector of 

 insects stated concerning the Lepidoptera at Bilbao that they 



^ F. Leydig, Ueber Verbreitung der Thiere im RhongeUrge tind Mainthal mil 

 Hinblick auf EifeUmd Rheinthal in Verhandliaigen des naturhistorischen Vereins 

 der preussischen Rheinlande und Westfalens, 1881, p. 156 et seq. 



2 Cf. the subsequent section on the relation of adaptation to the origin of 

 varieties among lizards. As long ago as 1874 {Lacerta muralis ccerulea) I con- 

 sidered moisture as having some effect in producing darkness of colour in these 

 animals. 



