332 TROPICAL NATURE, AND OTHER ESSAYS. 



In birds we meet with corresponding phenomena. 

 The most abundant and characteristic families of the 

 Old World tropics are replaced here by a series of 

 families of a lower grade of organisation, among which 

 are such remarkable groups as the chatterers (Cotingidse), 

 the manakins (Pipridse), the ant-thrushes (Formica- 

 riidse), the toucans (Rhamphastidse), the motmots 

 (Momotidae), and the humming-birds (Trochilidae), the 

 last perhaps the most remarkable and beautiful of all 

 developments of the bird-type. Parrots are numerous, 

 but these, too, are mostly of peculiar families ; while 

 pheasants and grouse are replaced by curassows and 

 tinamous, and there are an unusual number of remark- 

 able and isolated forms of waders. 



Reptiles, amphibia, fresh-water fishes, insects, and 

 land-shells, are all equally peculiar and abundant ; so that 

 South America presents, on the whole, an assemblage of 

 curious and beautiful natural objects, unsurpassed 

 perhaps even unequalled in any other part of the 

 globe. 



Past History of the American Continents. We will 

 now proceed to examine what is known of the past 

 history of the two American continents, and endeavour 

 to determine what have been their former relations to 

 each other and to the Old World, and how their existing 

 zoological and geographical features have been brought 

 about. And first let us see what knowledge we possess 

 of the past relations of North America with the Eastern 

 continents. 



If we go back to that recent period termed the Post- 

 Pliocene corresponding nearly to the Post-Glacial 

 period and to that of pre -historic man in Europe we 



