342 TROPICAL NATURE, AND OTHER ESSAYS. 



from Europe or North Asia in middle or late Tertiary 

 times, and have flourished there in consequence of a 

 less severe competition with highly-developed forms 

 of life. 



The birds of Australia and South America only exhibit 

 a few cases of very remote and general affinity, which are 

 best explained by the preservation in each country of 

 once wide-spread types, but is quite inconsistent with 

 the theory of a direct union between the two countries 

 during Tertiary times. 



Keptiles are even more destitute of proofs of any 

 such connection than even mammalia or birds ; but 'in 

 amphibia, fresh-water fishes, and insects the case is 

 different, all these classes furnishing examples of the 

 same families or genera inhabiting the temperate parts 

 of both continents. But the fact that such cases are 

 confined to these three groups and to plants, is the 

 strongest possible proof that they are not due to land- 

 connection ; for all these organisms may be transmitted 

 across the ocean in various ways. Violent storms of 

 wind, floating ice, drift-wood, and aquatic birds, are all 

 known to be effective means for the distribution of 

 these animals or their ova, and the seeds of plants. All 

 of them too, it must be noted, are to a considerable 

 degree patient of cold ; the reverse being the case with 

 true reptiles and land-birds, which are essentially heat- 

 loving ; so that the whole body of facts seems to point 

 rather to an extension of the Antarctic lands and islands 

 reducing the width of open sea, than to any former 

 union, or even close approximation of the Australian 

 and South American continents. 



