1900.] MUS SYLVATICUS AND ITS ALLIES. 397 



in Transylvania, while it only differs from the var. rupicola in 

 being unicoloured above. In fact the variety rupicola itself would 

 seem to be another case in point, being found, as it is in Lessona 

 and Pollinera, up to a height of 7000 feet in the Piedmontese Alps, 

 as well as in the Mourne Mountains of Ireland, from which it has 

 been recorded by Mr. W. D. Roebuck. 



From whatever point of view we regard the numerous forms 

 of Mus sylvaticus, it is of extreme interest to find that the 

 changes and variations in different climates are parallelled, to a 

 certain extent at least, not only by other mammals, but by birds 

 and, in some cases, by invertebrates. In a recent paper ' I 

 showed that the brightening of the colours of certain birds 

 according as they range southwards is parallelled by the Weasel, 

 Futorius nivalis Linnaeus and its subspecies. So, too, the most 

 richly coloured subspecies of Mus sylvaticus which I have seen is 

 Mus s. draco from Kuatun, a locality which must be near the 

 extreme south-eastern limit of the range of the species, while in 

 the south-west the deep, almost chocolate upperside of the single 

 British Museum specimen of M. s. algirus of Algeria seems to be 

 suggestive of a similar tendency. 



It is also of interest to find that the bright, clearly coloured Mus 

 sylvaticus of the cold drier regions of Central Europe is the counter- 

 part of the corresponding form of Squirrel, Sdurus vulgaris rufus 

 iverr ; whereas the duller subspecies of some of the damper Western 

 regions are parallelled by S. v. leucourus Kerr and S. v. typicus 

 Linnaeus ; and other parallels may be sought amongst the Red- 

 backed Voles (Evotomys) and their subspecies. We are only just 

 beginning to obtain any general light on the distribution of 

 ■variation amongst European mammals, but the larger size of 

 Mus s. princeps of Central Europe finds a parallel in at least one 

 other species, viz. Lepus europcms typicus Pall., of which the 

 Central European and Russian examples are distinctly larger than 

 the Western, L. e. occidentalis de Winton 2 . Indeed, it would be 

 easy to quote a good many other instances, taken from birds as well 

 as mammals, which seem to afford evidence of some law of decrease 

 in size from cold and clear to warmer and duller regions. Finally, 

 the occurrence of especially dark and often small forms in various 

 isolated western localities of the British Islands finds an abundant 

 counterpart in other groups. I may point to the Lepidoptera, 

 amongst which so many dark western varieties have been recorded ; 

 to the dark Squirrels of damp mountainous continental regions ; to 

 our small dark breeds of cattle (Scotch, Irish, and Welsh); and 

 to numerous instances amongst birds, as the Dippers (Cinclus) 

 and the Long-tailed Titmice (Acredula). Perhaps the most 

 interesting parallel of all is afforded by the Song-Thrush, Tardus 

 mimcus 3 , of which it is stated that individuals which inhabit the 



1 Ann. & Mag. Nat. Hist. (7) v. p. 42 (1900). 



2 See Mr. W. E. de Winton'9 paper, "On the Hare9 of Western Europe and 

 North Africa," in Ann. & Mag. Nat. Hist. ser. 7, vol. i. February 18D8. 



3 Howard Saunders, ' Manual of British Birds,' ed. iv. p. 3. 



