It is a law to which a large proportion of the organic creation would appear to be subject, that the exuberance of life (not so much, however, as regards the number of individuals which the various species may present, as in the grandeur of their size) has reference to the magnitude of the spot over which it is permitted to range. The unnatural breeding-in of a single race, which must of necessity happen unless the intercourse with other varieties of its kind be possible, has always been attended with effects more or less pernicious; and in the Annulose tribes I believe that the reduction of space which geological convulsions have at various epochs brought about, has been commonly succeeded (_inter alia_) by a reduction of stature in those species which have been cut off from their fellows. I do not assert that there are no exceptions to this rule; for counter-influences may at times prevail (as we shall shortly see), to neutralize the above tendency. I hold it, however, as an absolute truism, in physics, that a law without an exception is an anomaly. If, therefore, we were once to admit the latter to negative the former, no such thing as a law could exist. Hence it follows, as a corollary (unless, indeed, we are prepared to endorse that conclusion), _that_ _where there is a law there must be an exception to it_; and that, consequently, exceptional cases, if not exceedingly numerous, should never pervert our belief from an otherwise presumptive truth. This dwindling-down of size has seldom failed to attract my attention, more or less, in almost every island which I have hitherto had an opportunity of exploring: space, however, will not permit me to dwell upon many instances. I have already adverted to the diminished stature of _Anthonomus ater_, Mshm, and _Ceutorhynchus contractus_, Mshm, in Lundy Island,--the first of which scarcely ever reaches, on that rock, more than half its natural bulk. The late Mr. Holme, of Corpus Christi College, Oxford, in like manner, captured the common _Calathus melanocephalus_, Linn., and _Olisthopus rotundatus_, Payk., in Scilly,--the former of which seldom exceeded two lines, and the latter two and a half, in length: and he also recorded, that the _Bolitochara assimilis_, Kby, is invariably smaller in those islands than it is in the neighbourhood of Penzance[31]. The _Vanessa Callirhoe_, Fabr. (a geographical analogue of the Red Admiral Butterfly[32], so common in our own country), is permanently smaller in Porto Santo than it is on the larger, more luxuriant and varied, and therefore more protected, island of Madeira proper. And, as regards the _Ptini_ of that group, so completely are some of them "affected by isolation, and by exposure to a perpetually stormy atmosphere, that they do not attain half the bulk on many of the adjacent rocks that they do in the more sheltered districts of the central mass; and so marvellously is this verified in