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with a preponderance of Lamiidæ; and New Zealand 12, of which the Cerambycidæ are only slightly in excess.
The relations between the Longicorn fauna of the several regions, are such as are in accordance with the dependence of the group on a warm climate and abundant vegetation; and indicate the efficiency of deserts and oceans as barriers to their migration. The Neotropical and Australian regions have only 4 genera in common, but these are sufficient to show, that there must probably once have been some means of communication between the two regions, better adapted to these insects than any they now possess. The Nearctic and Neotropical regions have 5, and the Nearctic and Palæarctic 13 genera in common and peculiar to them, the latter fact being the most remarkable, because no means of inter-communication now exists, except in high latitudes where the species of the Longicorns are very few. The Oriental and Australian regions, on the other hand, are closely connected, by having no less than 52 genera of Longicorns in common and peculiar to them. Most of these are specially characteristic of the Malay Archipelago, often extending over all the islands from Sumatra to New Guinea. This large number of wide-spread genera of course gives a character of uniformity to the entire area over which they extend; and, with analogous facts occurring in other families, has led many entomologists to reject that division of the Archipelago between the Australian and Oriental regions, which has been so overwhelmingly demonstrated to be the natural one in the case of the higher animals. The general considerations already advanced in Chapter II. enable us, however, to explain such anomalies as this, by the great facilities that exist for the transfer from island to island of such small animals, so closely connected with woody vegetation in every stage of their existence. That this is the true and sufficient explanation, is rendered clear by certain additional facts, which those who object to the sharp division of the IndoMalay and Austro-Malay sub-regions have overlooked.
An analysis of all the Malay Longicorns proves, that besides the 52 genera characteristic of the Archipelago as a whole, there are 100 genera which are confined to one or other of its component
sub-regions. Many of these, it is true, consist of single species confined to a single island, and we will not lay any stress on these ; but there are also several important groups, which extend over the Indo-Malay or the Austro-Malay islands only, stopping abruptly at the dividing-line between them. For example, ori the Indo-Malay side we have Euryarthrum, Leprodera, Aristobia, Coelosterna, and Entelopes, and what is perhaps even more satisfactory, the large genera Agelasta and Astathes, abundant in all the Indo-Malay islands, but having only one or two species just passing the boundary into Celebes. On the other side we have Tethionea, Sphingnotus, Arrhenotus, Tmesisternus (the last three genera abounding from New Guinea to Celebes, but totally unknown further west), Hestima, Trigonoptera, Amblymora, Stesilea, Enes, and the large genus Micracautha, with but a single species beyond the boundary,—30 Austro-Malayan genera in all, each found in more than one island, but none of them extending west of Celebes. Here we have clear proof that the boundary line between the two great regions exists for Longicorns, as well as for all other animals; but in this case an unusually large number have been able to get across it. This, however, does not abolish the barrier, but only proves that it is not absolutely effectual in all cases. Those who maintain that the Malay Archipelago forms a single Coleopterous region, must disprove or explain the instances of limited range here adduced.
Out of nearly 1500 known genera of these insects, only one genus, Clytus, appears to be cosmopolitan. Saperda and Callichroma are the only others that perhaps occur in every region ; but these are both wanting over wide tracts of the earth's surface, Saperda being absent from Tropical Africa and the Malay Archipelago; and Callichroma from the Australian region, except one species in Polynesia. Many of the genera of Longicorns have a somewhat wide and scattered distribution, indicative of decadence or great antiquity. Mallodon and Parandra are mostly South American, but have species in Australia and Africa'; Oeme is found in Brazil and the United States, with one species in West Africa; Ceratophorus has 2 species in West Africa and 1 in New Zealand. Xystrocera is mostly African, but has single species in
Borneo, Java, Amboyna and South Australia ; Phyton has one species in North America and the other in Ceylon; Philagetes has 2 in South Africa, and 1 in Malacca: Toxotus abounds in North America and Europe, with one species away in Madagascar. Leptura is also North Temperate, but has a species at the Cape, one at Singapore and a third in Celebes. Necydalis has species in North and South America, Europe and Australia. Hylotrupes has 1 species in North America and Europe, and 1 in Australia ; Leptocera prefers islands, being found only in Ceylon, Madagascar, Bourbon, Batchian, the New Hebrides, New Caledonia and North Australia; Hathliodes is Australian, with 1 species in Ceylon; Schoenionta has 3 Malayan species, and 1 in Natal. Many other cases equally curious could be quoted, but these are sufficient. They cannot be held to indicate any close relation between the distant countries in which species of the same genus are now found, but perhaps serve to remind us that groups of great antiquity, and probably of great extent, have dwindled away, leaving a few surviving relics scattered far and wide, the sole proofs of their former predominance.
General Observations on the Distribution of Coleoptera. We have now passed in review six of the most important and best known groups of the Coleoptera or Beetles, comprising about 2,400 genera, and more than 21,000 species. Although presenting certain peculiarities and anomalies, we have found that, on the whole, their distribution is in very close accordance with that of the higher animals. We have seen reason to believe that these great and well-marked groups have a high geological antiquity, and by constantly bearing this fact in mind, we can account for many of the eccentricities of their distribution. They have probably survived changes of physical geography which have altogether extinguished many of the more highly organised animals, and we may perhaps gain some insight into the bearing of those changes, by considering the cross relations between the several regions indicated by them. On carefully tabulating the indications given by each of the groups here discussed, I arrive at the following approximate result. The best marked affinities between the regions are those between the Nearctic and Palæarctic,—the Oriental and Australian,
—the Australian and Neotropical,—which appear to be about equal in each case. Next comes that between the Ethiopian and Oriental on the one side, and the Ethiopian and Neotropical on the other, which also appear about equal. Then follows that between the Nearctic and Neotropical regions; and lastly, and far the least marked, that between the North Temperate and South Temperate regions. That the relation between the Ethiopian and Neotropical region should be so comparatively well marked, is unexpected; but we must consider that in such a comparison as the present, we probably get the result, not of any recent changes or intermigrations, but of all the long series of changes and opportunities of migration that have occurred during many geological epochs, probably during the whole of the Tertiary period, perhaps extending far back into the Secondary age.
It appears evident that Insects exhibit in a very marked degree in their actual distribution, the influence both of very ancient and very modern conditions of the earth's surface. The effects of the ancient geographical features of the earth, are to be traced, in the large number of cases of discontinuous and widely scattered groups which we meet with in almost every family, and which, to some extent, obscure the broader features of distribution due to the period during which the barriers which divide the several primary regions have continued to exist. And this, which we may consider as the normal distribution, is still further obscured in those cases where the barriers between existing regions are of such a nature as to admit of the free passage of insects or their larva in a variety of ways, and (what is perhaps of more importance) in which the physical features on both sides of the barrier are so nearly identical, as to admit of the ready establishment of such immigrants as may occasionally arrive. These conditions concur, for some families of insects, in the case of the Oriental and Australian portions of the Malay Archipelago: and it is there that the normal distribution has been sometimes greatly obscured, but never, as we have sufficiently shown, by any means obliterated.
AN OUTLINE OF THE GEOGRAPHICAL DISTRIBUTION OF MOLLUSCA.
The Mollusca being for the most part marine, it does not enter into the plan of this work to go into much detail as to their distribution. The orders and families will, however, be passed briefly in review, and all terrestrial and fresh-water groups discussed in somewhat more detail ; with the object of showing how far their distribution accords with that of the higher animals, and to what extent the anomalies they present can be explained by peculiarities of organisation and habits. If the views advocated in our fifth chapter are correct, the regions there marked out must apply to all classes of animals; and it will be the task of the students of each group, to work out in detail the causes which have led to any special features of distribution. All I can hope to do here, is to show, generally and tentatively, that such a mode of treatment is possible; and that it is not necessary, as it is certainly not convenient or instructive, to have a distinct set of “Regions” established for each class or order in the Animal and Vegetable Kingdoms.
For all the Marine groups I have merely summarised the information contained in Mr. Woodward's Manual of the Mollusca, but in the case of the Land Shells I have consulted the most recent general works, and endeavoured to give an accurate, though doubtless a very incomplete, account of the most interesting facts in their distribution. As their classification is very unsettled, I have followed that of the two latest great works, by Martens and Pfeiffer.