Clare Island Survey — Mammalia. 17 7 



able that these specimens should be indistinguishable from the typical 

 A. sylvaticus of Ireland generally, and of Great Britain. This indicates that 

 Clare Island cannot have received its Wood Mice at a very remote period, or, 

 in other words, that the island has only recently been severed from the 

 mainland. Further, there is no evidence that the Irish stock of Wood Mice 

 are ancient. Had they existed in Ireland for any great length of time, they 

 would surely have exhibited marked local distinctions, which they do not. 

 One can only suppose, then, that the Wood Mouse of Ireland is of about the 

 same age in that country as that of England, and that in both cases the period 

 of entry was subsequent to the period of entry into the Outer Hebrides,' 

 St. Kilda, and Fair Island. It is to be noted that the flavicollis stock is not 

 represented in Ireland, where is found only the smaller and more widely 

 distributed sylvaticus. If my argument be correct that the Wood Mice are 

 older in Britain than the Pygmy Shrew, and that the former are compara- 

 tively recent immigrants to Ireland (and southern England), it follows that 

 the Pygmy Shrew must be even more recent. Neither can have survived the 

 Glacial Period in Ireland. Neither can have been long isolated in Clare 

 Island. The mammals of that island point to its having been quite recently 

 severed from the mainland, or else they owe their presence there to 

 introduction. 



An objection may be raised that, the Wood Mice having been un- 

 doubted members of the Irish late pleistocene fauna, 2 as shown by excavations 

 in Irish caves, there is no reason why they should not have survived in 

 the country down to the present time, so that a few words on the 



1 Even allowing for the fact that complete isolation in a small island might give rise to more 

 rapid differentiation. 



2 This fauna is usually considered and called 'arctic' I do not use that word, as I do not 

 recognize a purely arctic Mammal -fauna. There is no evidence that the late pleistocene fauna was 

 of arctic origin ; it was formerly widespread and characteristic of its own period in northern Europe, 

 and its first connexion with arctic conditions was the purely incidental one of extermination or 

 expulsion thereby. On the termination of the Glacial Period, the shattered remnant of the so-called 

 ' arctic ' fauna encountered a new trial in the shape of the influx of a number of newer and more 

 vigorous mammals, which treated it even less gently than had the ice. The remnant again retired 

 or was driven out, in this case mainly northwards, where it has become popularly associated with 

 arctic conditions. The mammals of the arctic regions are of two kinds, viz., outlying members of 

 strong, dominant groups, such as wolves, bears, and stoats, which are vigorous enough to exist in any 

 known climate, and members of weak groups surviving in the Arctic because of the lack of 

 competition there with stronger forms, which, for one reason or other, have not penetrated to the 

 Arctic. Such are the Arctic Fox, the Varying Hares, the Lemmings, Reindeer, and Musk Ox. 

 Eventually such animals, after long sojourning in an atmosphere free from bacteria, become delicate, 

 and many, when transported south, find it difficult to resist the attacks of the organisms of such 

 diseases as pneumonia ; they may also become highly specialized to arctic conditions, an example of 

 which process is shown by the Greenland Hare, Boreolepits ffioeiifnuificus. 



