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Show ISLAND LIFE. (r.Alt'l' u: Locality. Latin Na1roe. English Name. 5. SALI\10 STOMAC!IIClJS · Gill a roo trout .. · .... · Black-finned trout .. Lakes of Ire1anJ. of Mountain lochs 6. , NlGRlPENNlS .. Wales and Scotland. L h Leven Loch OC 'ur· d Lomond, vv m er-nlere. N Loeh Leven trout ... 7. , LEVENENSlS ... L1n.nberris lakes, . 8. , PERISH ........ ·welsh eharr ........ .. Wo..les. L ke Windermere and a others in N. of Eng;l:: md, and Lake Brmach in Scotland. !). " WlLLUGilDII .. Windermere charr · · · 10. " KlLLINENSlS .. Lough Killin charr .. Killin lake in Mayo, Ireland. Lough Eske and Lough 11. " CoLn ·········· Cole's charr · .... · ·" ·" Dan, Ireland. . . Lough Melvin, Lettnm, GRAY I ..... N. W. Ireland. Gray's charr ········· 12. " . ... 13. Coru~aoNUS CLUPEOIDES The gwyniad, or schelly Loch Lomond, Ulleswater, Haweswater, and Bala lake. 14. " V.ANDESIUS 15. " POLLAN .... The vendace The pollan ........... . Loch Maben, Dumfriesshire. LOtwh Neagh and L~ugh Eurne, N. of Ireland. d'ff f 'each other and from These fifteen peculiar fishes 1 er rom. " l ur only but jn · 1 · s not 1n co o ' all British and contmenta spec1e ' l f rm and size of the such important structural charactersda;h~l~or~ or proportions of fins the number of the fin-rays, an . D Gunther ' bod or tail. They are 1U fact, as r. the head, y, d' t' t ecies as any other re-assures me, just as good Iand IS .mdc dspbe obiected that, until . d · f fi h t may In ee " cogmse species o s . d. . xplored and their fishes all the small lakes of Scan mabv1a are ethat w~ have any peculiar d · th we cannot e sure " com~are ;~t t~~;s~bjection has very little weight if we .consid'der species. k 1 ke and from Islan to how our own species vary from la e to a . d and . 1 d so that the Orkney species is not found In Scotlan ' . ~o~no~e of the peculiar British species extendsl.to I:el~;d, ~;h~~l~ 1 han six species altogether pecu Iar o I . lla.s no ess t . h d' t'nct what reason have ies of our own two Islands are t us IS 1 ' . spec1'or believincr that they will be otherwise than distmctffro~1 we 1' o 'th the amount o evithose of Scandinavia 1 At all events, WI of .deuce we c.tlready l1ossess of the very restricted ranges of many CHAP, XYI.] THE BRI'l'ISII ISLES. 32:3 our species, we must certainly hold them to be peculiar till they have been proved to be otherwise. The great speciality of the Irish fishes is very interesting, because it is just what we should expect on the theory of evolution. In Ireland the two main causes of specific changeisolation and altered conditions-are each more powerful than in Britain. Whatever difficulty continental fishes may have in passing over to Britain, that difficulty will certainly be increased by the second sea passage to Ireland; and the latter country has been longer isolated, for the Irish Sea with its northern and southern channels is considerably deeper than the German Ocean and the eastern half of the English Channel, so that, when the last subsidence occurred, Ireland would have been an island for some length of time while England and Scotland still formed part of the continent. Again, whatever differences have been produced by the exceptional climate of our islands will have been greater in Ireland, where insular conditions are at a maximum, the abundance of moisture and the equability of temperature being far more pronounced than in any other part of Europe. Among the remarkable instances of limited distribution afforded by these fishes, we have the Loch Stennis trout confined to the little group of lakes in the mainland of Orkney, occupying altogether an area of about ten miles by three; the Welsh charr confined to the Llanberris lakes, about three miles in length; Gray's charr confined to Lough Melvin, about seven miles long; while the Lough Killin charr, known only from a small mountain lake in Ireland, and the vendace, from the equally small lakes at Lochmaben in Scotland, are two examples of restricted distribution which can hardly be surpassed. Ca~tse of GTeat Speciality in Fishes.-The reason why fishes alone should exhibit such remarkable local modifications in lakes and islands is sufficiently obvious. It is due to the extreme rarity of their transmission from one lake to another. Just as we found to be the case in Oceanic Islands, where the means of transmission were ample hardly any modification of species occurred, while where these means were deficient and individuals once transported remained isolated during a long succession of ages, their forms and characters became so much changed as to y 2 |