CHAP. VIII 



CASES OF ADAPTATION 125 



the well-defined species of the best-known parts of the world 

 — Europe and North America — have paid more attention to 

 varieties, and especially to those characteristic of islands or 

 other well-marked and somewhat isolated districts. 



Having been much struck, some forty years ago, by the 

 fact that two peculiar beetles are found in Lundy Island (in 

 the Bristol Channel), another in Shetland, while some peculiar 

 forms of butterflies and moths occurred in the Isle of Man, 

 I thought it would be interesting to collect together and 

 publish lists of all the species or varieties of animals and 

 plants which had hitherto been found only in our Islands. 

 This I attempted when writing my Island Life in 1880, 

 and several specialists in various groups were kind enough 

 to draw up lists for me. These were revised and much in- 

 creased in the second and third editions ; and in the latter 

 (1902) they amounted to 5 birds, 14 fresh-water fishes, 179 

 lepidoptera, 71 beetles, 122 land and fresh -water molluscs, 

 and 86 flowering plants. It is interesting to note that of 

 these latter no less than 20 are found only in Ireland, where 

 the insular conditions of climate that may be supposed to 

 lead to modification are at a maximum. No less than 20 

 species of our Mosses and 27 of our Hepaticae are also not 

 found in Europe, though a few of them are (and others may 

 be) found in other parts of the world. 



As there is no doubt that our islands were at no distant 

 period (in a geological sense) united to the continent, and 

 that since their separation they must, through the influence 

 of the Gulf Stream penetrating around and among them, have 

 acquired a milder, moister, and a more uniform climate, 

 it seems quite probable that a considerable proportion of 

 these numerous local forms are actual modifications of the 

 allied continental forms due to adaptation to the changed 

 conditions. 



Since my book was published, an interesting addition to 

 the list of peculiar birds has been made by Dr. Ernst Hartert, 

 in an article entitled On Birds represented in the British 

 Isles by peculiar Forms. In this list, with MSS. additions 

 up to the end of 1909, Dr. Hartert enumerates no less than 

 24 species, which have become more or less distinctly 

 modified from their continental allies. These include a 



