The geographical distribution of animals, with a study of the relations ...
The geographical distribution of animals, with a study of the relations ... The geographical distribution of animals, with a study of the relations ...
;GG DISTRIBUTION OF ANIMALS. [part i.inconvenient. The one question then remains, whether theNearctic region should be kept separate, or whether it shouldform part of the Paleearctic or of the Neotropical regions.ProfessorHuxley and Mr. Blyth advocate the former course ;Mr.Andrew Murray (for mammalia) and Professor Newton (for birds)think the latter would be more natural. No doubt much is tobe said for both views, but both cannot be right ; and it will beshown in the latter part of this chapter that the Nearctic regionis, on the whole, fully as well defined as the PalaBarctic, by positivecharacters which differentiate it from both the adjacentregions. More evidence in the same direction will be found inthe Second Part of this work, in which the extinct faunas of theseveral regions are discussed.A confirmation of the general views here set forth, as to thedistinctness and approximate equivalence of the six regions, isto be found in the fact, that if any two or more of them are combinedthey themselves become divisions ofthe next lower rank,or " sub-regions " —and these will be very much more important,;both zoologically and geographically, than the subdivisions ofthe remaining regions,.It is admitted then that these six regionsare by no means of precisely equal rank, and that some of themare far more isolated and better characterized than others ; butit is maintained that, looked at from every point of view, theyare more equal in rank than any others that can be formedwhile in geographical equality, compactness of area, and facilityof definition, they are beyond all comparison better than anyothers that have yet been proposed forthe purpose of facilitatingthe study of geographical distribution. They may be arrangedand grouped as follows, so as to exhibit their variousrelations and affinities.Regions.jt ( Neotropical ... Austral zone Notogsea.°') Nearctic ) -n ,Boreal zonePai^arctic ...P1I Ethiopian P1 , . .Palaeogaea' 0riental jPalaeotropical zone\IJArctogaaa.\ Australian ... Austral zone Notogsea.The above table shows the regions placed in the order followedin the Fourth Part of this work, and the reasons for which are
chap, iv.] ZOOLOGICAL REGIONS. 07explained in Chapter IX. As a matter of convenience, and forother reasons adduced in the same chapter, the detailed expositionof the geographical distribution of the animals of the severalresions in Part III. commences with the Palsearctic and terminateswith the Nearctic region.Objections to the system of Circumpolar Zones.—Mr. Allen'ssystem of " realms " founded on climatic zones (given atp. 61), having recently appeared in an ornithological workof considerable detail and research, calls for a few remarks.The author continually refers to the " law of the distribution oflife in circumpolar zones," as if it were one generally acceptedand that admits of no dispute. But this supposed " law " onlyapplies to the smallest details ofdistribution—to the range andincreasing or decreasing numbers of species as we pass fromnorth to south, or the reverse ;while it has little bearing on thegreat features of zoological geography—the limitation of groupsof genera and families to certain areas. It is analogous tothe " law of adaptation " in the organisation of animals, bywhich members of various groups are suited for an aerial, anaquatic, a desert, or an arboreal life ;are herbivorous, carnivorous,or insectivorous; are fitted to live underground, or in freshwaters, or on polar ice.It was once thought that these adaptivepeculiarities were suitable foundations for a classification,—thatwhales were fishes, and bats birds ; and even to this clay thereare naturalists who cannot recognise the essential diversityof structure in such groups as swifts and swallows, sun-birds andhumming-birds, under the superficial disguise caused by adaptationto a similar mode of life.The application of Mr. Allen'sprinciple leads to equally erroneous results, as may be well seenby considering his separation of " the southern third of Australia" to unite it with New Zealand as one of his secondaryzoological divisions.If there is one country in the world whosefauna is strictly homogeneous, that country is Australia ;whileNew Guinea on the one hand, and New Zealand on the other,are as sharply differentiated from Australia as any adjacent partsof the same primary zoological division can possibly be. Yetthe " laiv of circumpolar distribution " leads to the division of
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chap, iv.] ZOOLOGICAL REGIONS. 07explained in Chapter IX. As a matter <strong>of</strong> convenience, and foro<strong>the</strong>r reasons adduced in <strong>the</strong> same chapter, <strong>the</strong> detailed exposition<strong>of</strong> <strong>the</strong> <strong>geographical</strong> <strong>distribution</strong> <strong>of</strong> <strong>the</strong> <strong>animals</strong> <strong>of</strong> <strong>the</strong> severalresions in Part III. commences <strong>with</strong> <strong>the</strong> Palsearctic and terminates<strong>with</strong> <strong>the</strong> Nearctic region.Objections to <strong>the</strong> system <strong>of</strong> Circumpolar Zones.—Mr. Allen'ssystem <strong>of</strong> " realms " founded on climatic zones (given atp. 61), having recently appeared in an ornithological work<strong>of</strong> considerable detail and research, calls for a few remarks.<strong>The</strong> author continually refers to <strong>the</strong> " law <strong>of</strong> <strong>the</strong> <strong>distribution</strong> <strong>of</strong>life in circumpolar zones," as if it were one generally acceptedand that admits <strong>of</strong> no dispute. But this supposed " law " onlyapplies to <strong>the</strong> smallest details <strong>of</strong><strong>distribution</strong>—to <strong>the</strong> range andincreasing or decreasing numbers <strong>of</strong> species as we pass fromnorth to south, or <strong>the</strong> reverse ;while it has little bearing on <strong>the</strong>great features <strong>of</strong> zoological geography—<strong>the</strong> limitation <strong>of</strong> groups<strong>of</strong> genera and families to certain areas. It is analogous to<strong>the</strong> " law <strong>of</strong> adaptation " in <strong>the</strong> organisation <strong>of</strong> <strong>animals</strong>, bywhich members <strong>of</strong> various groups are suited for an aerial, anaquatic, a desert, or an arboreal life ;are herbivorous, carnivorous,or insectivorous; are fitted to live underground, or in freshwaters, or on polar ice.It was once thought that <strong>the</strong>se adaptivepeculiarities were suitable foundations for a classification,—thatwhales were fishes, and bats birds ; and even to this clay <strong>the</strong>reare naturalists who cannot recognise <strong>the</strong> essential diversity<strong>of</strong> structure in such groups as swifts and swallows, sun-birds andhumming-birds, under <strong>the</strong> superficial disguise caused by adaptationto a similar mode <strong>of</strong> life.<strong>The</strong> application <strong>of</strong> Mr. Allen'sprinciple leads to equally erroneous results, as may be well seenby considering his separation <strong>of</strong> " <strong>the</strong> sou<strong>the</strong>rn third <strong>of</strong> Australia" to unite it <strong>with</strong> New Zealand as one <strong>of</strong> his secondaryzoological divisions.If <strong>the</strong>re is one country in <strong>the</strong> world whosefauna is strictly homogeneous, that country is Australia ;whileNew Guinea on <strong>the</strong> one hand, and New Zealand on <strong>the</strong> o<strong>the</strong>r,are as sharply differentiated from Australia as any adjacent parts<strong>of</strong> <strong>the</strong> same primary zoological division can possibly be. Yet<strong>the</strong> " laiv <strong>of</strong> circumpolar <strong>distribution</strong> " leads to <strong>the</strong> division <strong>of</strong>
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