332 



GEOGKAPIIICAL DISTEIBUTION OF SPECIES. [Ch. XXXVIII. 



man, whereas 



in all the 



mo 



are 



m 



marked 



distinctness in their dentition is accompanied by many other 

 differences ; snch as the prehensile tails belonging exclnsively 



mo 



World 



Australian marsupials. — The adherence to certain peculiar 

 types of structure observable in the animals inhabitino- dis- 

 tinct geographical provinces was illustrated in a still more 

 striking manner^ some time after the publication of Buifon's 

 great work, by the discovery in Australia of a group of mam- 



malia so unlike those of the 



World 



f" 



to be referable 



even to a distinct sub-class called the Marsupial, of wliich 

 there was only one genus previously known on the globe, 

 namely, the Opossum {Didelj)his) of America. Some of these 

 pouched animals, like the kangaroo, were herbivorous, others, 

 like the Tasmanian wolf {Thylacinus) carnivorous, and on the 

 whole they presented a parallel series in which were found 

 representatives of nearly all the grand divisions of the pla- 

 cental mammalia of the rest of the world. Mr. Waterhouse 

 has described about 140 species proper to the maifiland of 

 Australia, and about 9 others inhabiting New Guinea and 

 some neighbouring, islands of the Malay archipelago. 

 Among these, only one species, the flying opossum {Petaurus 

 ariel), is common to one of the islands and the continent. 



Geographical reloMon of extinct fossil forms to the nearest 

 allied living genera and species. — When we speculate on the 

 meaning of this restriction of a pecuhar division of the verte- 

 brata to a single province of the land, and try, by aid of it, to 

 gain some insight as to the plan which nature has followed in 

 peopling the earth with new species, we find ourselves in 

 some degree precluded from attributing the peculiarity of the 

 fauna to the nature of the climate, soil, and veo-etation of 

 Australia. It has at least been ascertained experimentally 

 that when placental mammalia of various orders^ whether 

 herbivorous or carnivorous — such as the ox^ the horse^ the dog, 

 and the cat — run wild in Australia, they are not only a match 

 for the native animals, but often obtain a mastery over them 

 and multiply greatly at their expense. How, then, does it 



r 



ii 



t 



hi: 



fo, 



