lIERPETOLOOY OF THE GRAND DUCHY OF BADEN. 141 



Perhaps the most intelligible of dark-coloured varieties are 

 those formed through adaptation to the environment (such as 

 many varieties of the Wall-lizard on the islands and continent 

 of Italy), for there is no difficulty in understanding how on black 

 volcanic ground, for instance, a dark race should have been 

 gradually preserved through the action of natural selection. 

 But in other melanic island forms of the same lizard (such as 

 L. Lilfordi) the colour is no more protective than in the many 

 analogous forms of other reptiles which are repeatedly being dis- 

 covered, but is due to an entirely different cause. Unfortunately, 

 all anatomical investigation has yet obtained but negative 

 results, but I venture to think undue importance has in some of 

 these cases again been attached to " moisture," whose effects 

 must necessarily be either more universal or nil. In some 

 more isolated instances of "melanism" among European 

 Lacertidce, the dark colour may possibly have been produced by 

 change of food, or some other physiological derangement, but it 

 appears to have spread over the body by the same method as in 

 the cases above alluded to, that is, by the gradual darkening of 

 the ground-tint, and not through the broadening out and fusion 

 of the original markings.* 



The var. nigriventris of L. muralis may be cited as an example 

 of partial melanism, for here, as the name indicates, the dark 

 colour is confined to the lower parts. In tracing out its course 

 of development, we see that the black is first visible in the shape 

 of minute spots on the throat, each scale of the collar being often 

 prettily marked with a black centre-piece. In Germany it is 

 frequently found in this stage of development, and sometimes 

 also in the next (transitional) stage, which consists in the entire 

 under surfaces being thus covered with minute spots, which 

 afterwards, in the true nigriventris, Bonap., expand to the 

 exclusion of all other colouring. It is noticeable that, in localities 

 where this variety has become dominant, the first gradation of 

 colour-development has been abbreviated, and the young already 



* Thus Gachet's black L. viridis is not an "advanced" maculata, if we 

 may judge by what he says: — "Apres avoir ete plonge pendant plusieurs 

 jours dans l'alcool, . . . . les grosses taches noires, dont on ne voyait que 

 des traces, sont devenues tres-apparentes " (Act. d. 1. Soc. Linn, de Bordeaux, 

 1833, p. 168). 



