THE STUDY OF BIOLOGY. 29 



Why, then, should the kangaroos and their marsupial kith and kin 

 stop short at "Wallace's Line" ? The answer to this query involves 

 considerations which extend over the whole domain of life-science. 

 The briefest possible explanation of the kangaroos' distribution must 

 therefore suffice for our present purpose. Let us go back in imagina- 

 tion to that far-back time in the history of our earth when the 

 Triassic rocks were being formed. That period existed ages before 

 the Chalk in point of time. It was the period, moreover, when the 

 first quadrupeds appeared on the earth's surface. These primitive 

 animals were wholly of marsupial kind, and entirely of the type of 

 which our kangaroos and other Australian mammals are the existing 

 representatives. Not a single higher mammal, thus graced the Triassic 

 forests ; no elephants roamed in Triassic jungles j the plains of these 

 early times were unenlivened by the agile deer, or by the grace of the 

 antelope herds j no carnivora roamed about to slay and devour the 

 weaker races ; and the humblest quadrupeds were lords of animal 

 creation, and represented in themselves the fulness of the mammalian 

 life which the later ages were destined to see. 



Over the whole land surfaces then in existence these low 

 marsupial quadrupeds of the Trias in due course spread. In 

 Britain, on the Continent, in the New World, the fossil remains of 

 these early Triassic quadrupeds are found ; the best known of them 

 being represented most nearly by the little "banded ant-eater" 

 (Myrmecobius) living in Australia to-day. In the Triassic period, 

 also, Australia obtained its marsupials. For that island-continent 

 was then part of the Asiatic or Palsearctic mainland, and the con- 

 necting land was not then broken up into the islands of the Eastern 

 Archipelago of to-day. 



The next phase in the drama of Australian quadruped-life shows 

 us that, at the close of the Triassic and of the succeeding Oolitic 

 periods, that land became disjointed from the mainland. Geological 

 change made Australia the island-continent we see it to-day. And 

 what of its quadrupeds ? These early marsupials, left to themselves, 

 shut off from all possible invasion by and competition with higher and 

 later quadrupeds, flourished and grew apace in the Australian land. 

 Elsewhere, and in the rest of the world, the early marsupials were 

 distanced in the "struggle for existence" which ensued on the 

 evolution of higher types of life. Elsewhere than in Australia, they 

 were killed off ; and at the close of the Oolite age (or that immediately 

 succeeding the Trias) hardly a remnant of the great marsupial life of 

 these two periods was left to bear witness to the first beginnings of 

 mammals on the earth. In Australia how different was, and still is, 

 the quadruped-life ! In the "recent " bone-caves of Australia we meet 

 with the remains of giant marsupials, compared with which the 

 largest kangaroo of to-day appears a pigmy form. These are the 



