INTRODUCTORY REMARKS. xliil 



phasis of certain insular phenomena, in which nearly every detached 

 islet appears on first investigation to add its own particular "species" 

 to the general list ; and certainly it seems to me to offer a clue to 

 much that might otherwise be unintelligible in the fauna of this 

 scattered archipelago. 



In estimating the action of physical changes in the earth's surface 

 on its fauna, I would not wish to give them an undue importance, 

 or to exclude a consideration of the countless other methods by 

 which species may (and have) become established on even the re- 

 motest rocks, where, be it observed, they would be as much subject 

 to the same modifying influences as if they had been left there by 

 some overwhelming geological crisis. Yet in ventilating all such 

 questions, it is not by the assumption of " general laws " (which are 

 sometimes imaginary), but by the actual evidence before us, that we 

 are compelled at last to form our judgment; and I must confess 

 that all the varied means of dispersion (often so anomalous and 

 unlooked-for) do not appear to me, in these Atlantic islands, to have 

 done much (if indeed anything) towards determining the present 

 distribution of the truly endemic species. Yet a natural catastrophe, 

 on a scale sufficiently gigantic to break-up a continuous land which 

 was already stocked with its own aboriginal organisms, would in all 

 probability lay the foundation of phenomena (as regards the latter) 

 exactly parallel to what we now meet with in the various component 

 parts of these oceanic Groups. 



Although it is true that numerous slight modifications, or insular 

 states (for the most part unimportant), appear to have been brought 

 about (probably at a very remote epoch) in many of the species, I 

 can detect no trace of anything like a law of development which 

 could be regarded as still operating to intensify (however gradually) 

 the peculiarities of the forms which now exist. On the contrary, 

 indeed, if there is one thing which strikes us more than another, it 

 is their permanence, or apparent freedom from all tendency to fur- 

 ther change, the extremely sedentary nature, and phlegmatic habits, 

 of a large proportion of them (as in the case of Deucalion and most 

 of the Tarpldi) seeming almost to place them beyond the influence 

 of those external circumstances and conditions which might be sup- 

 posed to have some infinitesimal power over the outward configura- 

 tion of creatures which are more nervously organized. Amongst the 

 Land-shells, indeed (in which the insular races are still better de- 

 fined, and also far more numerous, in proportion to the extent of 

 the fauna, than is the case amongst the Coleoptera), this fixedness of 



