EDWARD FORBES. 207 



present day is found inhabiting a larger or smaller ' specific 

 area;' and there is found in that area one point the 

 'metropolis' of the species where the individuals are 

 more abundant than elsewhere, and which may therefore 

 be taken as the point where the species was originally 

 created. As a matter of course, no species could have 

 more than one 'specific centre.' If, therefore, a species 

 should be met with in two quite detached areas as 

 sometimes happens this must be explained on the 

 supposition that the original area of the species had 

 become divided into two in consequence of changes in 

 the physical geography of the area. Or, it might be 

 supposed that some individual of the species had been 

 accidentally transported from its original area to some 

 new place, where the conditions happened to be suitable 

 for its existence and propagation. 



Forbes further believed that when a species had once 

 become extinct, it was never re-created. We sometimes 

 find, however, that a given species, after living a long time 

 in some particular region, disappears altogether from that 

 area, and that, after a longer or shorter period, it reappears 

 again in the same place. This phenomenon was explained 

 by Forbes on the supposition that the species had been 

 forced to abandon its original area, in consequence of 

 some change of conditions which rendered its further 

 existence there impossible, and that it had therefore 

 migrated to some adjoining area where it met with 

 suitable surroundings. At a later period, however, the 

 conditions of the original area might again become 

 favourable to the species, and then it would migrate back 

 again. In this case, therefore, there is no real extinction 



