214 FISHES. 



2. Which of them are to be considered to be autochthont 

 species, that is, forms which came ia the tertiary epoch or 

 later into existence within the area to which they are still 

 limited, or from which they have since spread? 



3. Which are the forms which must be considered to be 

 immigrants from some other region ? 



The mode of division of the earth's surface into zoological 

 regions or areas now generally adopted, is that proposed by 

 Mr. Sclater, which recommends itself as most nearly agree- 

 ing with the geographical divisions. These regions are as 

 follows : — 



I. PALiEOG^A. 



1. The Paloearctic region ; including Europe, temperate 



Asia, and North Africa. 



2. The Ethiopian region ; including Africa, south of the 



Sahara, Madagascar, and the Mascarene Islands; 

 also Southern Arabia. 



3. The Indian region ; including India south of the 



Himalayas, to Southern China, Borneo, and Java. 



4. The Australian region ; including Australia, the Pacific 



Islands, Celebes, and Lombock. 



II. Neog^a. 



5. The Nearctic region ; including North America t,o 



Northern Mexico. 



6. The Neotropical region ; including South America, the 



West Indies, and Southern Mexico. 



Comparatively few classes and orders of animals have 

 been carefuUy studied with regard to their geographical 

 distribution, but the majority of those which have been 

 examined show that the difference of latitude is accompanied 

 by a greater dissimilarity of indigenous species than that of 



