70 THE WANDERINGS OF ANIMALS [OH. 



beasts and others which have an almost world-wide 

 range and yet are much more scarce than their 

 nearest allies. For instance, ravens compared with 

 crows. Some kinds exist in literally countless mil- 

 lions, others perhaps only in thousands. About these 

 numbers of individuals we know nothing ; the only 

 species of which a rough census has been made is 

 man. But for some conspicuous animals we can at 

 least calculate a rough upper limit. It is unlikely 

 that there exist, or have ever existed, more than 

 one million lions in the whole of Africa, because we 

 can construct their annual food-bill, etc. and thus 

 narrow the probabilities. The existing stock of 

 orang utans in Borneo has been guessed at 50,000. 

 Countless species have died out whilst others 

 have come on, a process which is still at work, but 

 from a broad point of view (omitting local fluctua- 

 tions) the general impression of a fauna is that the 

 relative and actual numbers of the individuals hold 

 their own, that there is neither an undue increase 

 nor a marked decrease. How this balance of nature 

 works is in well-nigh every case an absolute mystery. 

 This is due to our ignorance of the economics, the 

 complex correlations, of every animal and plant. 

 We do not know them of ourselves. Every kind of 

 animal, living under favourable conditions (and 

 nearly all live only where they find such), would 

 in the natural course of events increase its numbers 



