CHAP. XVI THE BRITISH ISLES 330 



To this cause we must impute our comparative poverty 

 in mammalia and reptiles — more marked in the latter 

 than the former, owing to their lower vital activity and 

 smaller powers of dispersal. Germany, for example, 

 2^ossesses nearly ninety species of land mammalia, and 

 even Scandinavia about sixty, while Britain has only 

 forty, and Ireland only twenty-two. The depth of the 

 Irish Sea being somewhat greater than that of the 

 German Ocean, the connecting land would there probably 

 be of small extent and of less duration, thus offering an 

 additional barrier to migration, whence has arisen the 

 comiDarative zoological poverty of Ireland. This poverty 

 attains its maximum in the reptiles, as shown by the 

 folio win Of fissures : — 



Belgium has 22 species of reptiles and amphibia. 



Britain ,,13 



Ireland ,,4 ,, ., :, 



Where the power of flight existed, and thus the period 

 of migration Avas prolonged, the difference is less marked ; 

 so that Ireland has seven bats to twelve in Britain, and 

 about 110 as against 130 land-birds. 



Plants, which have considerable facilities for passing 

 over the sea, are somewhat intermediate in proportionate 

 numbers, there being about 970 flowering plants and ferns 

 in Ireland to 1,425 in Great Britain, — or almost exactly 

 two-thirds, a proportion intermediate between that pre- 

 sented by the birds and the mammalia. 



Peculiar British Birds. — Among our native mammalia, 

 reptiles, and amphibia, it is the 023inion of the best 

 authorities that we possess neither a distinct species nor 

 distinguishable variety. In birds, however, the case is 

 different, since some of our species, in particular our 

 coal-tit and long-tailed tit, present well-marked differences 

 of colour as compared with continental specimens; and 

 in Mr. Dresser's work on the Birds of Buropc they are 

 considered to be distinct sj^ecies, while Professor Newton, 

 in his new edition of Yarrell's British Birds, does not 

 consider the differencer to be sufficiently great or suffi- 

 ciently constant to warrant this, and therefore classes 



Z 2 



