18 



ISLAND LIFE. 



[part I. 



while allied species come to the north bank, which in like 

 manner forms their boundary. As examples we may mention 

 that one of the Saki monkeys (Pithecia monachus 1 ) comes up 

 to the south bank of the Upper Amazon, while immediately 

 we cross over to the north bank we find another species 

 (Pithecia rufibarhata 1). Among birds we have the green 

 jacamar (Galhula viridis), abundant on the north bank of the 

 Lower Amazon, while on the south bank we have two allied 

 species (G-alhula rufoviridis and G. cyaneicollis) ; and among 

 insects we have at Santarem, on the south bank of the Ama- 

 zon, the beautiful blue butterfly, Callithea sapphira^ while almost 

 opposite to it, at Monte-alegre,an allied sipedes, Callithea Zeprieuri 

 is alone found. Perhaps the most interesting and best known 

 case of a series of allied species, whose ranges are separate but 

 conterminous, is that of the beautiful South American wading 

 birds, called trumpeters, and forming the genus Psophia. There 

 are five species, all found in the Amazon valley, but each 

 limited to a well-marked district bounded by great rivers. On 

 the north bank of the Amazon there are two species, one in its 

 lower valley extending up to the Rio Negro, and the other in 

 the central part of the valley beyond that river ; while to the 

 south of the Amazon there are three, one above the Madeira, 

 one below it, and a third near Para, probably separated from 

 the last by the Tocantins river. 



Overlapping areas among the species of a genus is a more 

 common phenomenon, and is almost universal where these 

 species are numerous in the same continent. It is, however, 

 exceedingly irregular, so that we often find one species extend- 

 ing over a considerable portion of the area occupied by the 

 genus and including the entire areas of some of the other 

 species. So little has been done to work out accurately the 

 limits of species that it is very difficult to give examples. One 

 of the best is to be found in the genus JDendrosca, a group of 

 American wood-warblers. These little birds all migrate in the 

 winter into the tropical regions, but in the summer they come 

 north, each having its particular range. Thus, D. dominica 

 comes as far as South Carolina, D. ccerulea to Virginia, I), dis- 

 color to Southern Maine and Canada; four other species go 



