INTRODUCTION 3 



primarily in three natural divisions (which may, in fact, 

 be considered as Sub-classes) of nearly equal value. These 

 three Sub-classes are, as named by Professor Huxley — the 

 Prototheria, embracing only the Order Monotremata — 

 the Metatheria, equivalent to the Order Marsupialia, and 

 the Eutheria, which includes all the remaining Orders 

 from the Edentata to the Primates. Let us, therefore, 

 consider the distribution of the members of these three 

 Sub-classes on the earth's surface. When we come to 

 examine the ranges of these groups on the map, we 

 shall find that the Monotremes are wholly confined to 

 Australia and New Guinea; that the Marsupials pre- 

 dominate in Australia, and are only met with elsewhere in 

 South America (one or two species of Opossum occurring 

 in North America, but being probably only recent in- 

 truders from the south) ; and that the typical mammals or 

 Eutheria occupy the rest of the world. 



Again, after examining the distribution of the seven 

 Orders of typical mammals, we remark the following 

 significant facts : — 



1. The absence of Insectivores in South America. 



2. The great prevalence of Edentates in the same 

 country; the Sloths, Armadilloes, and Ant-eaters, consti- 

 tuting three out of the five known families of this Order, 

 being entirely confined to South and Central America. 



Taking these main facts as our guide, we may divide the 

 land-surface of the Earth as follows, into three divisions : — 



fl) Land where Marsupials" 

 prevail ; no Euther- 

 ians except Rodents 

 and Bats ; Mono- 

 tremes 



Australia, New Guinea | „ 

 and the adjacent islands, j 



