32 QEOGEAPHICAL DISTRIBUTION. 



strictly confined to the tropical regions of the earth's surface, but 

 few forms. being found beyond the limits of that zone. They are 

 fau-ly abundant in the forest region of South America, ranging 

 from Paraguay to Mexico, and less so in South and Southeast 

 Asia, and some of the islands of the Malay Archipelago. In Af- 

 rica the family is represented by but two species. The Psitta- 

 cidae among parrots furnish us with another good example of a 

 divided family, whose members are to be found only in the two 

 great southern continents, Africa and South America, and in some 

 of the adjacent islands. Still more remarkable is the case of the 

 ostriches, of which there are two species (of the genus Struthio) 

 pertaining to the desert regions of Africa and Western Asia (Arabia 

 and Syria), and likewise two (of the genus Rhea, sometimes placed 

 in a distinct family) belonging to tem.perate South America, whose 

 range extends from Patagonia to the confines of Brazil. 



Among reptiles similar instances are presented by the tropi- 

 copolitan groups. Thus, we have the Crocodilidae inhabiting the 

 tropical waters of both the Eastern and Western Hemispheres. The 

 PythonidEe, or giant constricting serpents — ^boas, anacondas, pythons 

 — are, with the exception of the Californian genus Charina, some- 

 times referred to this family, distinctively tropical, but they have 

 representatives in the South American continent, in Africa, Asia, 

 Australia, and in several of the continental and oceanic islands. 

 The family of iguanas (Iguanidae), comprising upwards of fifty gen- 

 era and some three hundred species, is almost distinctively Ameri- 

 can, being distributed from about the fiftieth parallel of south 

 latitude, in Patagonia, to the Canadian boundary-line on the north. 

 No member of the family is known from either of the continents 

 of Eurasia or Africa, yet the family crops up again in a solitary 

 genus— Brachylophus— in the Feejee Islands, and two (doubtfully 

 placed) genera have also been described from Madagascar and Aus- 

 tralia. 



Distribution of Orders. — The principal features of geographical 

 distribution exhibited by species, genera, and families repeat them- 

 selves in a measure in the case of the higher groups of the animal 

 kingdom known as orders. Very narrowly circumscribed areas of 

 habitation, at least among the orders of higher animals, do not 

 exist ; broad distribution is the rule. Among mammals the most 

 marked instances of semi-localisation, if so it may be termed, are 



