28 



NATURE 



S^Nov. 13, 1873 



THE COMMON FROG* 

 IV. 



HAVING now passed in review the greatest differences 

 presented by the nearest allies of our common frog 

 (the members namely of its own order), certain facts of 

 interest present themselves respecting the geographical 

 distribution of the group. These facts are interesting, 

 because they point not only to the exceptional nature of 



the faunas of South America and of Australia, but also to 

 a certain zoological affinity between those two regions of 

 the earth, distinct as they are from one another. Thus, 

 as has been mentioned, it is only in Australia and South 

 America that the typical genus Rana is absolutely wanting. 

 One genus of Tree-frogs, Pelodryas, is confined to Aus- 

 tralia, but is closely resembled by another genus, Pliyllo- 

 incdiisa, which is restricted to South America, and differs 

 from the former only by the absence of a web between 



Fig, 16. — An American Eft of the genus AmblysU 



the toes. It should be recollected that the primary sub- 

 divisions of a zoological order are VtrnxeA /ami lies. One 

 whole family, called Cyslii;natlii(hr, is (with the exception 

 of two species) confined to Australia and America. 



The typical Tree-frogs (//i'/(?) abound in South America 

 and are also found in Australia, but not in India or in 



Africa south of the Sahara. On the other hand another 

 genus of Tree-frogs (Polypedates), is found in India, 

 Japan, and Madagascar, but not in either Australia or 

 America. 



The typical Toads {Bufd) have, however, their head- 

 quarters in South America, yet are wanting in Australia, 



though they are found everywhere else where the order 

 exists at all. 



The earth's surface, considered as to its population of 

 the frog and toad order, may be divided into three great 

 regions. The first of these is composed of Europe, 

 Northern Asia (with Japan and Chusan), North America, 



and Africa north of the Sahara. The second region 

 consists of Africa south of the Sahara, Madagascar, 

 India, and the Indian Archipelago. The third region is 

 made up of South America and Australia, and the resem- 

 blance between these two parts of the earth's surface as 

 to their frogs and toads is paralleled by that as to their 



mammalian faunas, since marsupial mammals (orpouched- 

 beasts of the opossum kind), are strictly confined to 

 Australia (and its islands) and America. 



No Frog or Toad has yet been found in New Zealand. 



Africa, considering its size and climate, is poor in spe- 

 cies of Afiou/ii. 



We should be prepared for the fact that in South 



" Continued from p. 13. 



America Tree-frogs abound, since all kinds oJ animals in 

 that region assume an arboreal habit. 



Monkeys are tree-livers all the world over, but nowhere 

 are all the indigenous species so thoroughly arboreal as in 

 tropical America. There alone do we find monkeys with a 

 prehensile tail capable of serving as a fifth hand, and so 

 affording greater security and facility to locomotion amidst 

 the branches. Only there also do we find beasts so ex- 



