140 THE ZOOLOGIST. 



the phenomenon of black or sombre tints is so common with 

 widely- separated classes of animals that we are driven to assume 

 some general cause producing it. And, by way of hypothesis, to 

 explain some of these facts, Prof. Eimer has suggested the direct 

 effects of the "former dampness"* in the atmosphere, and is 

 evidently disposed to see in the present colour of the embryo of 

 L. vivipara (which has been "retained" by the melanic adults) 

 that of its ancestors in the post-glacial period. But in the case 

 of several higher alpine animals which equally tend to "melan- 

 ism," this can hardly be admitted a vera causa, and it is almost 

 as easy to imagine — while we are in nubibus — that in this 

 instance the glacial epoch itself favoured, indirectly, the pro- 

 duction of black, by preserving those individuals who could best 

 retain warmth through means of dark-coloured fur. At the 

 cessation of extreme cold the majority would re-assume more 

 protective coloration, while those remaining in the Alps and 

 other secluded localities would continue less liable to lose this 

 tendency. Perhaps in this period can be placed the acquisition 

 of viviparous habits by Pelias berus, as well as the origin of the 

 singular development of Salamandra atra and other peculiarities 

 of alpine forms. With L. vivipara, as well as Anguis frag His and 

 Pelias berus, the females incline more to variability of this 

 description, and in the first-named it is therefore easy to assume 

 a tendency to revert to ancestral coloration, though this hardly 

 explains the matter satisfactorily. And, speaking of reptiles in 

 general, we are unable in the vast majority of cases to account 

 for the frequent appearance of "melanism." We see that there 

 are many grades of this condition, from a scarcely appreciable 

 difference in the normal coloration to complete blackness, and 

 that all these gradations are frequently displayed by one species ; 

 and further, that while most species exhibit some individual 

 variability of this character, the tendency has in others led to 

 the production of melanotic varieties, possessing often a local 

 preponderance over the typical form. It also becomes evident 

 that this form of coloration spreads over the body in different 

 ways, and is induced or favoured by various, not always external, 

 causes, for the investigation of which the microscope alone is of 

 little value. 



* ' Variieren der Mauereidechse,' p. 200, 



