CASES OF ADAPTATION 135 



iN'ortli America — have j^aid 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 ^Alan, I 

 thought it would be interesting to collect together and publish 

 lists of all the species or varieties of animals and plants whicli 

 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 increased 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 inter- 

 esting 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. Xo 

 less than 20 species of our Mosses and 27 of our Ilepaticse 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 Ilartert, 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 21 spe- 

 cies, which have become more or less distinctly modified from 



