Reviews — Dr. R. F. Scharf—Eurojwan Fauna. . 525 



has orii^in:\te(l. The capture of a swallow-tail or of a inavhled white 

 butterfly in England at once furnislies material for reflection as to 

 the reason of its absence from Scotland and Ireland. Why should 

 the nightingale allow its beautiful song to be heard in England, 

 and never stray across the Channel to the sister isle or cross the 

 borders of North Britain? Lovers of bird-life and sportsmen, who 

 have observed the habits of the ptarmigan in the wild mountain 

 recesses of Scotland, are aware that nowhere else in the British 

 Islands do we meet with this interesting member of the grouse 

 family, and many no doubt have allowed their minds to dwell upon 

 the causes of its singularly local distribution. 



"AH these animals have a wide range in other parts of the world. 

 In past times, before man began to make observations on the 

 geographical distribution of birds and butterflies, or even before 

 the appearance of man in Northern Europe, they may have lived 

 all over the British Islands. For some reascm or other they are 

 perhaps dying out or withdrawing towards their original home, 

 which may either be northward or to the east or south. If we had 

 some clue as to their former history from fossil evidence — or, in 

 other words, if their remains had been preserved to us in geological 

 deposits — we should have less difficulty in deciding this problem. 

 But butterflies are scarcely ever preserved in a fossil state, and birds 

 very rarely. We know little or nothing, therefore, of their past 

 history from direct evidence, and are obliged to trust to indirect 

 methods of research, which will be indicated later od. 



" Mammals and snails tell their story more plainly. The bones of 

 the former and the shells of snails are easily preserved, and thus 

 furnish us with the necessary data as to their past history, for we 

 find them abundantly in most of the recent geological deposits. 

 Among the mammals of the British Islands there are some instances 

 of distribution wdiich much resemble those I have quoted. Thus 

 the Arctic Hare (Lepns variahilis) is in the British Islands confined 

 to Ireland and to the mountains of Scotland ; and if it were not lor 

 the fact that its bones have been discovered in a cave in the south- 

 west of England, we should perhaps never have known that, 

 formerly, it must have inhabited that country as well. Of other 

 mammals we possess fossil and also historical evidence of their 

 having once lived in these Islands, such as the wolf and the wild 

 boar, both of which were abundant in Great Britain and Ireland. 

 The latter is a distinctly southern species. We assume this because 

 its remains have never been found in high northern latitudes ; nor 

 does it now occur in Northern Europe or Northern Asia, whilst all 

 its nearest relatives live in sub-tropical or tropical climates. The 

 Arctic Hare, on the contrary, has probably come to us from the 

 north. Its remains are unknown even in Southern Europe, and 

 the more we approach the Arctic regions the more abundant it 

 becomes. Thus we have here two instances of British mammals, 

 one of which, the wild boar, has died out, as it were, in a southerly 

 direction ; whilst the other, the Arctic Hare, is apparently retreating 

 tort'ards the north. 



