INTRODUCTION. 3 
Borneo, or its continuation which runs between Lcmbock on 
the east, and Bali, at the extremity of Java, on the west, we 
shall find all the islands lying to the westward of that line 
devoid of Marsupials, and possessing a Mammalian fauna closely 
akin to that of India. The line of the channel in question is, 
therefore, evidently a very important one as regards distribu- 
tional zoology; and since this importance was first clearly 
demonstrated and explained by the great explorer and natural- 
ist, Dr. A. R. Wallace, it is now by common consent appro- 
priately denominated “‘ Wallace’s line.” To the eastward Marsu- 
pials extend as far as New Ireland and the Solomon Islands, 
but they are unknown in Polynesia proper, as, indeed, they are 
in New Zealand, where, by the way, save for a few Bats and 
perhaps a Rat, there are no indigenous Mammals at all. 
Such is, roughly speaking, the general distribution of the 
Marsupials of the Australian region. It must not, however, be 
supposed that the group is confined to that part of the world, 
although it there attains a much greater development than 
elsewhere. As a matter of fact, a single family of Marsupials 
—namely, the Opossums—is found throughout the wooded 
districts of Central and South America, extending southwards 
to the open pampa of Argentina, and represented in North 
America by a single species which ranges as far north as the 
Hudson river and Missouri. ‘These Opossums, which, by the 
way, must not be confounded with the so-called Opossums 
(really Phalangers) of the Australian colonists, are all car- 
nivorous, but differ widely in structure from the members of the 
group inhabiting Australia. That they were originally Old 
World forms is proved by the occurrence of their fossil remains 
in the middle Tertiary deposits of England and other parts of 
Europe, where Marsupials allied to those of Australia are now 
_ unknown. If, however, we descend deeper in the geological 
_ Scale, and reach the lower portion of that great series of rocks 
B 2 
