206 GEOLOGICAL DISTKIBUTION. 



mammoth on the supposition that it was swept off by unknowably 

 great glacial floods following in the wake of the northern ice-sheet, 

 has as yet little to sujiport it. Why just the mammoth should 

 have been thus swept away, when other animals, like the reindeer, 

 contemporaries of the mammoth, and like it animals of the frozen 

 north, survived, is not very comprehensible.* The extinction of 

 the musk-ox in Europe and its survival in America offers a no less 

 remarkable puzzle to the biologist. 



That very frequently what may appear to be insignificant causes 

 are sufficient to bring about extermination is shown in the case of 

 many of the largest, and seemingly most resisting, animals. The 

 arrested numerical development of the Indian elephant has been 

 attributed by Dr. Falconer, a competent authority, to the unceas- 

 ing harassings of insect pests, a view which was also shared by Bruce 

 with respect to the elephant of Abyssinia. And we are assured, 

 on the authoritjf of Darwin, that "insects and blood-sucking bats 

 determine the existence of the larger naturalised quadrupeds in 

 several parts of South America." The ravages of the tze-tze among 

 the South African ruminants has long been commented on by trav- 

 ellers, and the "plague" of the mosquito is only too familiar to 

 require special consideration. Humboldt has gTaphically delineated 

 the numerous circumstances, including inundations, parched vege- 

 tation, ravages of wild beasts, and the like, which in many of the 

 grassy regions of South America threaten the destruction of both 

 cattle and horses, and these, or similar ones, exist over most parts 

 of the earth's surface. In short, a perpetual check is placed upon 

 the free increase of all classes of organisms, the overcoming of 

 which displays the measure of success in the universal struggle for 

 existence. We know of no law which by itself determines the 

 duration of life in any group of organisms, or which exjilains why 



* The mammctli, although its remtiins are most abundantly found in the 

 far north, cannot riirlitly be classed as an exclusively northern animal, as is 

 proved by tlie discovery of its bones in reajions as far south as Santander, in 

 Spain, and Eorae, in Italy. Indeed, it is not exactly impossible, as is claimed 

 by Boyd-Dawkins (" Early Man in Britain," p. 108), that the modern In- 

 dian elephant is only a varietal form of this species which, through long 

 hal)ltation in the tropical or semi-tropical forests, has lost some of those minor 

 cliaractcristies, such as the coating of hair or wool, which serve in a general 

 way to distinguish the nortliern animal. If this be true, then the mammoth 

 would still be a member of our existing fauna. 



