22 THE GEOGRAPHY OF MAMMALS 



Section IV. — The Austral Sub-region 



The " island-continent " of Australia, as Mr. Wallace 

 terms it, has, as has now been positively ascertained, a 

 large portion of its interior so parched up and barren as to 

 be almost destitute of animal life. But all along the east 

 and south-east coasts, where there is land of sufficient 

 elevation to condense the vapours from the adjoining 

 ocean, more fertile districts are found. Besides the more 

 widely diffused Australian types, some peculiar forms are 

 met with only on this side of the continent. Tasmania, 

 which is, in fact, but a recently separated piece of this 

 portion of Australia, has also a moister and less extreme 

 climate, and contains representatives of many of the 

 special Australian forms, besides some indications of an 

 autochthonous fauna. 



The most peculiar mammals of Australia, and those 

 which first claim our attention, are its representatives of 

 the two forms which together constitute the Sub-class of 

 Monotremes. These are the extraordinary genera Orni- 

 thorhynchus and Echidna, which in their toothless jaws, 

 in the conformation of their sternum and shoulder girdle, 

 and especially in the structure of their reproductive organs, 

 exhibit unmistakable signs of divergence towards the Classes 

 of Reptiles and Amphibians. The first of these, usually 

 known to the colonists as the " Duck-bill " or " Water-mole," 

 (see Fig. 1, p. 23) is entirely aquatic in its habits, and is met 

 with only in the streams and waterholes of New South 

 Wales and Tasmania, where it burrows in the banks, and 

 swims and dives with great facility. The Echidna, or 

 " Spiny Ant-eater," is more widely distributed, and, as we 



