ABSENCE OF CERTAIN SPECIES.

301 the islands, which determines these. In this respect, as we have already explained in the chapter on Climate, Guernsey is the typical district. Jersey is, in fact, pre-eminently French, and Sark somewhat less intermediate than might be expected. Guernsey, in other words, is the most of an island; Jersey the most of a peninsular portion of the terra firma of France. Amongst butterflies, the grapta C. album has contrived in its excursions from the Continent to reach Jersey, where it is by no means scarce; it has yet, however, to find its way to Guernsey and Sark. It may be, that although originally present in all the islands, the conditions favourable for its preservation have been removed by the more perfect insulation that has been produced in the more distant islands in course of time, causing the species to die out. Whatever the reason may be, however, the absence of this species amongst others marks a significant fact. It is from the due consideration of such facts in sufficient number and variety that generalisations are made, and the physical geography and ancient history of physical change of the islands explained and illustrated.

Compared with many other isolated tracts of equal extent, the Channel Islands are rich in both species and individuals; and they are this, so far as they are continental as well as insular. Compared with many other isolated districts, they are characterized by the continental character of their species; or rather, they are conspicuously characterized by the absence of anything peculiar and special to themselves. So far as they are this, they are also continental,-continental of the continent of France.

Concerning the doctrine that the bulk or size of individual animals is encouraged by the conditions which a continent, and discouraged by those which an island presents, a doctrine (or rather complex of doctrines) more especially connected with the researches of Mr. Wollaston-what say the Channel Islands? Mr. Wollaston, considering the diminution in the size of beetles

302

CAUSES OF MODIFICATION OF SIZE.

in detached islands, refers it to the constant and repeated breeding from the same stock. That the bulk of the facts which he has with great care and much discursive investigation brought to bear on his doctrine are realities, is as transparently true as it is true that the doctrine itself is an hypothesis. The question whether certain animals in small islands lose size from the simple fact of breeding in-and-in is one thing, and the question whether they lose size at all, irrespective of the reason why, is another. The latter is the primary one. Every fact, however, commands its due amount of attention; and if there were only one insect in one island which, on the strength of its being an insular representative of a continental species, had been subservient to either the verification or the confirmation of a legitimate hypothesis, no observer would be justified in ignoring the line of enquiry which it suggested. He need not be a naturalist, ex professo, to do it. He need only be able to keep his eyes open for certain facts, and when any one of the kind required came within his ken, to make a note of it. There is no need for any writer who (happening to know that the entomology of Lundy Island, the Flat Holmes, and the Scilly Isles, have been studied with a view to certain phenomena) is also writing about the Channel Islands, to excuse himself for lookingout for such relevant facts as he can appreciate, and for laying them before the reader as he finds them.

The model way of working some of the problems suggested by the statement that the bulk of individuals falls off in insular localities, would be to take (say) a hundred weight of continental and a hundred weight of insular beetles, or butterflies, and get the difference (if there were one) in gross. But this is what ought to be rather than what is. Nor if it were otherwise, could certain preliminary cautions be dispensed with. It is the opinion of a good and competent observer that butterflies and moths reared in the ordinary way, from the caterpillar state in confinement, are, as a rule, smaller than those caught. Now in the

COMPARISON OF INDIVIDUALS.

303

Guernsey collections most of the specimens have been reared this way, and it is clear that this fact may so far influence the result, as to destroy the value of the generalisation. On the other hand, the same naturalist states that, by special attention to feeding, insects may be obtained actually larger than those in a state of nature. As some collections are made from larvæ kept in confinement, and some from insects caught in the perfect state, it is clear that without much preliminary caution as this, no weight and no measure, no individual observation and no mass of averages, would be of any scientific value.

Bearing in mind these possibilities, we may proceed to allude to a few facts that seem to have a bearing on the question at issue.

In the following short list, the first table contains such butterflies as, allowing for the exceptions already suggested, appear, on a careful inspection, combined with a comparison, of more collections than one, to be larger, as individuals, than their equivalents in England; the second, those which, similarly viewed, seemed smaller.

To which add (from Moths) urapterix sambucaria, which a pre-eminently trustworthy collector has never found equal to the English measurements.

There is just a fragment of a system in this: the large Coliades being French and South-English, rather than truly British, butterflies; the small species of vanessa and grapta being thoroughly English, and (as is instanced by the absence of grapta C. album in Guernsey, though found in Jersey) only in part insular. There is a fragment, then, of a system in the evidence as far as it goes; just enough to guard against generalization and to stimulate to wider and more minute enquiries.

304

EXISTENCE OF OVERLAPPING ZONES.

Pieris daplidice, like grapta C. album, although found in Jersey, has yet to be discovered in Guernsey. Considering that it is taken on the coast of Kent, and even in the neighbourhood of Brighton, its absence is remarkable. Unless the south-coast specimens crossed the Straits of Dover, or unless there were certain inordinately favourable winds, their presence in Sussex and their absence in Guernsey is strange.

The polyommatus bæticus-a variety in each locality—has also been found at Brighton as well as in Guernsey. On the 5th of August, 1860, Mr. Newman, junior, forwarded it to Mr. Doubleday, who determined the species; and Mr. Newman, senior, thus notices it:-"The species is common on the Continent, and was seen in profusion along the northern coast of France, and in the Channel Islands."

Speaking generally, the characteristic species of the islands are not precisely those of France, and by no means those of England. Still, the West of England, as it approaches Guernsey in climate, does not depart widely either in its Fauna or Flora. As has been intimated in the valuable remarks by Dr. Bowerbank, quoted in the account of the sponges, there is a kind of overlapping zone in the outlying islands of Guernsey and Sark; so that these localities include much that is peculiar both in north-western Europe and south-western England and Ireland.

The result of generalisations concerning these and other species that exhibit differences, whether between the different islands or between the islands and France, may be stated in a very few words. They bear upon the important inquiry, as to whether the islands are portions of an old continent, gradually diminishing, or of a new continent, gradually increasing.

This question may be considered as settled very positively by the lists presented in the chapters on Botany and Zoology. There is too much resemblance to the natural history of Western Europe, and too large a number of species, to justify any

NO GREAT MODERN SUBSIDENCE.

305

one in suggesting the bare possibility that they belong to a rising mass of land, receiving its species by migration across water. The number of species is so very large in all departments, and in all the islands, that the separation from the main land is not only certain, but must have been an event recent in the ordinary geological sense of that expression.

The very remarkable state of the land and sea bottom in the open gulf or bay in which are the rocks and islands we have been describing, coupled with some apparent historical evidence, the value of which will be considered in another chapter, has, however, induced a suspicion among many persons, both English and French, that an important depression of European land in the neighbourhood of the Channel Islands, took place so recently as about the end of the eighth century; and again, others less considerable, at many subsequent times, amounting in all to as much as 150 feet.*

At present, then, it must be sufficient to state in general language, that the zoology and botany of the island, as far as they are known, do not support such a view. The islands have no doubt been detached from France, recently enough in one sense, but not in the historic sense. Nor does it seem probable, that since the introduction of the prevailing species any of the islands have existed at a very different level, whether higher or lower, from that they now have.

While on the one hand there is no biological or historical evidence of this great depression, or of the recent separation of the islands from the main land, or from each other, so, on the other hand, is there no geological evidence of recent subsidence.

This view is adopted by M. de Quatrefages in the book already referred to, and is evidently favoured by other writers, although no tangible arguments are brought forward. A gentleman residing in Jersey is about to publish evidence to the same purport, which he considers sufficient to justify the conclusion which is here controverted, and which will be noticed somewhat more fully in a subsequent chapter on the archæology of the islands.

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