No. 537] ZOOGEOGRAPHY OF THE EAST INDIES 541 



rather attempts to explain the reasons for the peculiari- 

 ties of their distribution. At first men sought the ex- 

 planation especially in climatologic factors, or else they 

 considered each zoogeographic region to be a particular 

 center of special creation. Finally the theory of evolu- 

 tion in this, as in so many other subjects, spread a new 

 light. Zoogeography lias become, then, especially since 

 it came under the leadership of Wallace, an essentially 

 historical study. 



Every type of animal has come into existence upon 

 some specially circumscribed part of the earth, and has 

 spread itself thence over a greater or lesser extent of 

 surrounding territory. Only very seldom does it happen 

 that one spreads itself over the whole earth or even 

 a considerable part of it; the great majority are hin- 

 dered by unsurmountable obstacles, and inhabit only a 

 limited region. Zoogeography, then, on the one hand, 

 must deal with the means of dispersal, and on the other 

 hand with the hindrances which species may encounter. 



These obstacles are, in general, spoken of as being of 

 a climatic or orographic nature. The latter are not sur- 

 prising; for if the surface of the earth were homogene- 

 ous in character, then the animals would naturally have 

 distributed themselves in girdles or zones at even dis- 

 tances from the equator. Indeed, this is to a consider- 

 able extent the case with the marine fauna, against the 

 spread of which such hindrances as we have mentioned 

 play a minor role. Thus we can differentiate and recog- 

 nize an arctic, a circumtropical, and an antarctic zone 

 (Ortmann). The Indopacific Ocean, obviously belong- 

 ing to the circumtropical belt, is faunistically a single 

 entity, and to this our archipelago belongs. 



While in earlier times climate and natural conditions 

 were held as being most answerable for differences in 

 land and fresh-water faunas, they far more slowly took 

 the orographic factors at their true value; though nat- 

 urally the first-named influences must not now remain 

 unheeded. 



Great deserts, high mountain ranges, and extensive 



