26 



ISLAND LIFE. 



[part I. 



birds which are truly cosmopolites ; but there are many genera 

 of hawks, owls, wading, and swimming birds which have a 

 v/orld-wide range. 



As a great many genera consist of single species there is no 

 lack of cases of great restriction, such as the curious lemur called 

 the " potto " which is found only at Sierra Leone, and forms the 

 genus Perodicticus ; the true chinchillas found only in the Andes 

 of Peru and Chili south of 9° S. lat. and between 8,000 and 

 12,000 feet elevation ; several genera of finches each confined to 

 limited portions of the higher Himalayas, the blood-pheasants 

 (Ithaginis) found only above 10,000 feet from Nepal to East 

 Thibet ; the bald-headed starling of the Philippine islands, the 

 lyre-birds of East Australia, and a host of others. 



It is among the different genera of the same family that we 

 meet with the most striking examples of discontinuity, although 

 these genera are often as unmistakably allied as are the species 

 of a genus ; and it is these cases that furnish the most interest- 

 ing problems to the student of distribution. We must therefore 

 consider them somewhat more fully. 



Among mammalia the most remarkable of these divided 

 families is that of the camels, of which one genus Camelus, 

 the true camels, comprising the camel and dromedary, is con- 

 fined to Asia, while the other, Auchenia, comprising the llamas 

 and alpacas, is found only in the high Andes and in the plains 

 of temperate South America. Not only are these two genera 

 separated by the Atlantic and by the greater part of the land of 

 two continents, but one is confined to the Northern and the 

 other to the Southern hemisphere. The next case, though not 

 so well known, is equally remarkable ; it is that of the Centetidae, 

 a family of small insectivorous animals, which are wholly con- 

 fined to Madagascar and the large West Indian islands Cuba and 

 Hayti, the former containing five genera and the latter a single 

 genus with a species in each island. Here again we have the 

 whole continent of Africa as well as the Atlantic ocean separat- 

 ing allied genera. Two families of rat-like animals, Octodon- 

 tidse and Echimyidse, are also divided by the Atlantic. Both are 

 mainly South America, but the former has two genera in North 

 and East Africa, and the latter also two in South and West 



