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although he makes many complimentary allusions to Mr. Allen and his views, he employs in nearly all its entirety the system adopted in this work, with the exception that he recognises an Arctic Sub-region to include the more northerly parts of both the Old and New worlds.
Finally, Professor Newton, who has given us his views on this subject as regards birds (7), adopts the method of divisions followed here with the two following exceptions. In conformity with the suggestion already made to Professor Heilprin, he unites the Palæarctic and Nearctic Regions under the title “Holarctic," and he also separates New Zealand from Australia as an independent region.
The chief questions in dispute, therefore, seem to be as follows:
(1) Whether the Palæarctic and Nearctic Regions are to be recognised as separate ?
(2) Whether Madagascar and New Zealand are to be separated as independent regions from the Ethiopian and Australian Regions respectively ?
(3) Whether the Ethiopian and Oriental Regions should be joined to form one region ?
(4) Whether there are any good grounds for dividing the Neotropical into two separate regions.
The only way in which questions of this sort could be settled would be by constructing accurate lists of the families and genera of the various classes of the terrestrial faunas of the regions in dispute, and then carefully comparing them, in order to determine the percentage of peculiar species and of absentees. The difficulty of doing this satisfactorily is twofold.
(1) The absence of any definite boundaries to most of the regions, and hence the difficulty in determining how many of the border-forms, which have obviously intruded from the neighbouring regions, should be counted.
(2) The uncertainty as to the limits of the genera. This uncertainty has been greatly increased of late years by the action of some zoologists in proposing a multitude of unnecessary generic terms.
When these two factors have been settled and the lists constructed, a further difficulty is met with, and this is one which depends very much on the individual fancy of the author, namely, as to the percentage of peculiarity which should be required to constitute a Region.
Taking the first question in dispute, we find that Mr. Allen, in his paper already quoted (2), gives a tabulated list of the genera of his North Temperate realm, dividing them into North American and Eur-asiatic (=Palæarctic) forms, and putting the individual genera into three categories, namely, those circum-polar, or common to the Nearctic and Palæarctic Regions (numbering thirty-two); those peculiar to each Region (i.e. twenty-nine to the Nearctic and forty-one to the Palæarctic); and, finally, those which
range further south into the Neotropical Region on the one hand, and into the Oriental and Ethiopian Regions on the other.
Working from these tables we find that 38 per cent. of the Nearctic genera and 42 per cent. of the Palæarctic genera are confined to their respective Regions, while 42 per cent. in the case of the Nearctic and 34 per cent. in the case of the Palæarctic are common to the two regions. These last percentages include, however, several quite widespread genera which can hardly be called circum-polar—such as Sciurus, Sciuropterus, Lepus, Lutra, Canis, and Felis.
These figures show that there is, as has indeed never been disputed, a great amount of similarity between the Nearctic and Palæarctic faunas, but not enough to justify the junction of these two great land-masses into one “Region ” or “Realm.”
As for the so-called “ Arctic realm,” which consists of the land bordering the Polar Ocean and Hudson's Bay and the great peninsula of Greenland,“ beyond the limit of arboreal vegetation,” together with the similar Arctic portion of the old world, Mr. Allen states, no doubt correctly, that it contains a “homogeneous hyperborean fauna of circum-polar distribution.” But looking to the extreme poverty of life in these inclement latitudes, as Mr. Allen well puts it, it seems to be quite unnecessary to elevate this wretched fraction of the Earth's surface into one of its principal constituent life-regions. The plan adopted by Mr. Wallace, of regarding it as a borderland between the Nearctic and Palæarctic Regions is far preferable.
The question of the recognition of Madagascar and New Zealand as independent regions will be further discussed in the articles on the Ethiopian and Australian Regions respectively, as will also the propriety of dividing the Neotropical into two separate regions. A few words, however, may be said here with regard to Mr. Allen's proposal to join together the Oriental and Ethiopian Regions into one “Realm."
According to the estimate given below (Table I., p. 16), the total number of genera found in the Oriental Region is 113, and of these thirty-nine are not found elsewhere. Of the balance—seventy-four-eight only are common to the Oriental and Ethiopian Regions, and are not found in any other Region, whereas twenty-eight more, also known in the Oriental and Ethiopian Regions, are likewise found in the Palæarctic Region. Furthermore, out of the eight genera above mentioned, although they are not now found in the Palæarctic Region, four of them are known to have existed there during the Pliocene period. This shows, we think, very conclusively that what small resemblance there is between the mammals of the Oriental and Ethiopian Regions is due rather to a similarity in their origin, than to any sort of direct connection between the two regions.
1 These are Manis, Rhinoceros, Elephas, Golunda, Atherura, Viverra, Mellivora, and Nycteris.
To sum up the subject we add a table of the numbers of orders, families, and genera of mammals found in the six different Regions, together with the number of genera confined to them (endemic), the number of those slightly transgressing the Regional borders (quasi-endemic), and the number of those of wide-spread distribution in each Region. In the second table these numbers have been reduced to percentages, which give in some respects a better idea of the relative specialisation of the mammalfauna of each Region. On examining these tables, it will be seen that the Ethiopian Region stands second in point of the number of genera confined to it, coming next to the Neotropical Region.
The lists of genera from which this table has been worked out are based on those adopted in Flower and Lydekker's (3) standard work on mammals, with a certain number of additions and corrections. In consequence of this the figures in the case of the Nearctic Region will not be found to exactly correspond with those quoted from Mr. Allen above (2). It must also, of course, be understood that the figures are merely approximate, and liable to continual alterations as new discoveries are made.
Approximate Numbers of Families, Genera, and Species of
Mammals in the six Regions.
Numbers given in Table 1. reduced to Percentages of Total
Numbers of Families and Genera.
The groups entirely confined to each region are classed as “endemic”; those that cross the frontiers slightly as “quasi-endemic"; all others are considered as "wide-spread."
The percentages, it will be observed, on account of the omission of fractions, do not exactly make up one hundred in every case.