G2 MR. A. MUHEAT on the GEOQIIAPHIOAL BELATIOKS OF 



having got into positions where their retreat has been cut off by 

 a change in the physical conditions of the country *. In like 

 manner we can point out the Australian intruders at the Cape, 

 the Cape element in Patagonia and without difficulty detect 

 certain Brazilian settlers, which I shall presently mention as 

 having made their way into West Africa. This, at first sight, 

 seems difficult of apprehension and inconsistent with the wide 

 spread of the very same species in other countries. Here are a 

 few Staphylinidso lingering at the Cape or at Angola without 

 having succeeded in penetrating into West Africa, altliough, so 

 far as we can judge, they have been there for many geological 

 epochs ; while other or the same genera of Staphyliuidae have in 

 the short period siuce the retreat of the glacial epoch covered the 

 north of Europe, Asia, and America with their hordes. There is 

 something more here than mere physical barriers standing in the 

 way of their dispersal. The explanation is simple : when the 

 land fitted for their occupation is left free and unoccupied, as the 

 northern half of Europe, Asia, and America was after the glacial 

 epoch, the new comers cover the ground like wildfire, and the 

 fauna and flora is rapidly' established. When the ground is once 

 occupied the case is different ; every new comer meets the most 

 stubborn resistance, the battle for life is resolutely contested, and 

 the small proportion that we find established shows that few make 

 good their entrance at aU, and still fewer make any progress in tlieir 

 new land : and the truth may be that, instead of looking upon a 

 scanty infiltration of an alien element into a land as an indication 

 of its having been very ancient and almost washed away by repeated 

 dilution (as we liave generally been disposed to do), we should re- 

 gard it only as an indication of a more recent attack on a well -gar- 

 risoned laud which has successfully repelled the intruders. This is 

 a consideration which throws additional light upon the enormous 

 power and importance of the counterpoises of nature,— without 

 them aland instantly taken up, with them the established order of 

 things inpenetrable to all assaults — not an encouraging reflection 

 to revolutionists, if the same rule prevails in the moral world 

 which exists in the material world, which we cannot doubt to be 

 the case. The students of geographical distribution may likewise 

 * The Berlin Museum has obtained from Mr. Van cTer Decken's expedition, 

 a true Carabus from Mount Kilimandjaro. It is the only Carabus that has yet 

 been found in Africa proper, is peculiar in form (elytra swollen and rounded), 

 but in other respects more in the direction of C. alpinus of Switzerland than any 

 thing else. It is obviously a European form whose retreat has been cut off. 



