April 26, 1894] 



NA TURE 



61 



older regions. I have already shown that this is the case with 

 the almost cosmopolitan plovers, and it also occurs in another 

 instance where it has been very strongly urged that the Sclaterian 

 regions will not apply. I allude to the distribution of insects in 

 the Oriental and Australian portions of the Malay Archipelago. 

 Here, in the case of birds and mammals, there is a most abrupt 

 and striking change on passing from Borneo and Java to the 

 Moluccas and New Guinea ; but in insects this is not con- 

 spicuously the case, and it has been said that the whole Archi- 

 pelago, from Sumatra to New Guinea, and even to the Solomon 

 Islands, is characterised by one uniform insect -fauna. This, 

 however, is by no means a correct statement. There are un- 

 doubtedly many genera common to the whole Archipelago, as 

 might be e.xpected from the great similarity of climate and the 

 uniformly forest-clad nature of the islands, together with the 

 power of crossing narrow seas possessed by all winged insects. 

 Yet, both among butterflies and beetles, especially the latter, 

 there are a considerable number of genera confined respectively 

 to the Indo-Malayan and Austro-Malayan divisions of the Archi- 

 pelago, giving to the fauna of each a characteristic facies. 



Now if we adopt for insects, as has been proposed, a single 

 Malayan regionincludingthe wholeofthe Archipelago, we should 

 be apt to lose sight of the two distinct elements it contains, the 

 one due to an ancestral diversity corresponding to that which still 

 exists in all the higher animals, the other dependent on a com- 

 paratively recent process of intermigration between the two 

 portions of what are fundamentally distinct insect faunas ; while 

 it is not clear what corresponding advantage would be obtained 

 by the student of geographical distribution. 



From the point of view I have now endeavoured to set forth, 

 we may, I think, draw the conclusion that the six Sclaterian 

 regions are natural zoological divisions, because they are 

 separated by barriers of considerable antiquity and permanence, 

 which have led to their being characterised each by well-marked 

 assemblages of the higher animals. Further, when groups of 

 organisms which from their exceptional powers of dispersal, or 

 from any other cause, have been able to extend themselves 

 beyond these barriers, that is no reason whatever for establish- 

 ing new regions — which would not be marked out by equally 

 important barriers — since the divergencies in the distribution of 

 the various classes or orders, as exhibited by means of a common 

 series of regions, is one of those interesting problems of dis- 

 tribution which can only be solved by comparative study. Not 

 only, therefore, is one set of regions all that is required to ex- 

 hibit the distribution of the various terrestrial organisms : but, 

 for all purposes of comparative study it is immeasurably 

 superior to the establishment of numerous sets of special regions, 

 constructed so as to accord with the distribution of special 

 animal groups. 



We now come to the second objection — the supposed in- 

 equality of the six Sclaterian regions. Some of them are said 

 to be really only sub-regions, while others are said to be so diverse 

 as to be rendered more equal if divided into two regions. 



This question of equality is decided almost exclusively by 

 one characteristic, and one that seems to me to be not the most 

 important for the purpose we have in view. This character is 

 the possession of peculiar groups of the rank of family or 

 order, taking no account either of the richness and variety of 

 life-development, or of the geographical extent of the area in 

 question. From this point of view Australia is sometimes said 

 to be equal to all the rest of the world, both on account of its 

 rich development of the marsupial order, but especially because 

 in the duck-bill and spiny ant-eater it possesses a distinct sub- 

 class of mammals. From another point of view, however, 

 Australia, Africa, and South America are united in one primary 

 region, because they alone possess one of the sub-classes of 

 birds — the Ratitse. 



New Zealand and Madagascar have each been proposed as 

 regions, the first on account of its Apteryx and moas, with its 

 isolated lizard-like Hatteria ; the second for its peculiar families 

 of Lemurs and Insectivora, and equally peculiar families and 

 genera of birds. In contrast with these, we have the proposal 

 to unite the rich and extensive Palcearctic and Nearctic regions 

 to form one region only, because they do not possess a sufficient 

 number of peculiar families and genera of mammals and 

 birds, although the new region thus constituted is perhaps 

 twenty times as rich as New Zealand in varied forms of 

 life. 



NO. 1278, VOL. 49] 



Those who adopt these views appear to me to attach a very 

 exaggerated importance to the possession by a limited area of 

 some remnant of an otherwise extinct group, which has been 

 preserved owing to its long-continued isolation in a district 

 where it has been secure from the competition of higher forms — 

 almost always, therefore, in an island. Such survivals are ex- 

 ceedingly interesting ; but I cannot see what they have to do 

 with the division of the whole land-area of the globe into 

 zoological regions, whose sole purport and use is to facilitate 

 the study of the geographical distribution of all lam^ 

 animals. 



The conception of zoological regions expressed in the views 

 I am now combating seems to me to be altogether erroneous, 

 and to lead to results which are neither useful nor instructive, 

 and far less natural than that which takes account of a variety of 

 characters as the best guides to an approximate equality. I 

 urge, therefore, that zoological regions, to be at once natural and 

 useful in the highest degree, must be founded on a combination 

 of essential features, as follows : — 



(i) They should be founded upon, and approximate to, the 

 great primary geographical divisions of the earth, which there is 

 reason to believe have been permanent during considerable 

 geological periods. 



(2) They should be rich and varied in all the main types of 

 animal life. 



(3) They should possess great individuality ; whether ex- 

 hibited by the possession of numerous peculiar species, genera, 

 or families, or by the entire absence of genera or families 

 which are abundant and widespread in some of the adjacent 

 regions. 



Tested by these conditions the six Sclaterian regions seem 

 all that can be desired — subject of course to modification in de- 

 tails. If we make some allowance for the inevitable poverty 

 of the temperate as compared with the tropical regions — due 

 both to present and to past conditions of climate — they present a 

 greater amount of equality than might be expected. The Neo- 

 tropical region is somewhat the richest— very much the richest 

 in birds and insects — and this may be traced to its possessing so 

 enormous an area of tropical forest-clad land, together with the 

 greatest of the mountain ranges situated wholly within the 

 tropics — the Andes, and two other isolated mountain groups of 

 great extent and antiquity in Brazil and Guiana ; while the Ne- 

 arctic is the poorest — due perhaps to its rather limited area, its 

 large extent of arid lands, but more especially to its extreme 

 climate, a severe winter prevailing to considerably south of the 

 parallel of 40° N. Latitude. 



The subdivisions of the primary regions is far less important ; 

 and with the same facts before them, naturalists arrive at dif- 

 ferent conclusions. I would suggest, therefore, that for the pre- 

 sent, at all events, no definite named subdivisions should be 

 attempted, but that the continental portion of each region be 

 subdivided by the use of the terms north, south, east, west, and 

 central, with their combinations where required. By the use of 

 these terms the range of a genus or species within the regions may 

 be defined with sufiicient accuracy, and in a manner at once 

 intelligible to every student. 



The conclusions to which this discussion has led us may now 

 be briefly summarised as follows : Zoological regions are those 

 primary divisions of the earth's surface of approximately conti- 

 nental extent, which are characterised by distinct assemblages of 

 animal types. Though strictly natural, in the sense already 

 pointed out, they have no absolute character as equal inde- 

 pendent existences, since they may have been different in past 

 a^^es, but are more or less conventional, being established 

 solely for the purpose of facilitating the study of the existing 

 geographical distribution of animals in its bearing on the theory 

 of evolution. There is thus, in my opinion, no question of who 

 is 7-ight and who is wrong in the naming and grouping of these 

 regions, or of determining what are the true primary regions. 

 All proposed regions are, from some points of view, natural, 

 but the whole question of their grouping and nomenclature is 

 one of convenience and of utility in relation to the object 

 aimed at. 



It is because I think that the future progress of a branch of 

 biological study in which I take great interest will depend on 

 our arriving at some uniformity of view as to this question of 

 zoological regions, that I have devoted so much space to its 

 discussion. 



