The geographical distribution of animals, with a study of the relations ...

—174 ZOOLOGICAL GEOGRAPHY. |>art in.South America, Australia, and South Africa with Madagascarhave been more or less completely isolated, during long periods,both from the northern continent and from each other. Theselatter countries have, however, been subject to more or less immigrationfrom the north during rare epochs of approximationto, or partial union with it. In the northern, more extensive, andprobably more ancient land, the process of development hasbeen more rapid, and has resulted in more varied and highertypes ; while the southern lands, for the most part, seem to haveproduced numerous diverging modifications of the lower gradesof organization, the original types of which they derived eitherfrom the north, or from some of the ancient continents in Mesozoicor Palaeozoic times. Hence those curious resemblances inthe fauna of South America, Australia, and, to a less extent,Madagascar, which have led to a somewhat general belief thatthese distant countries must at one time or other have beenunited ; a belief which, after a careful examination of all thefacts, does not seem to the author of this work to be wellfounded. Oh the other hand, there is the most satisfactoryevidence that each southern region has been more or lessclosely united (during the tertiary or later secondary epoch)with the great northern continents, leading to numerous resemblancesand affinities in their productions.In endeavouring to present at a glance in the most convenientmanner, the distribution of the families in the several regionsand sub-regions, it was necessary to arrange them, so that thosewhose relations to each other were closest should stand side byside ;the first and last being those between which the relationswere least numerous and least important. Influenced by theusual opinions as to the relations between Australia and SouthAmerica, the series was at first begun with the Nearetic, andterminated with the Australian and Neotropical regions ; and itwas not till the whole of the vertebrate families had been gonethrough, and their distribution carefully studied, that these lasttwo regions were seen to be really wider apart than any othersof the series. It was therefore decided to alter the arrangement,beginning with the Neotropical, and ending with the Australian