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THE AMERICAN NATURALIST [Vol. XL 



travelers to the contemporary rhinoceroses, and were equal to the 

 modern elephant type. This therefore may be considered as a 

 contributory cause rather than as one of the chief causes of titano- 

 there extinction. 



The Inadaptation of Large Size 



There is a widespread belief, which is not borne out by the 

 facts, that bulky animals have tended to disappear first. 



Thus Owen, although as late as LS77 ^ disposed to attribute the 

 extinction of the laroc manunals of Australia to the agency of man, 

 advanced tlH> theory - of llic (Usud vantages of bulky size imder 

 changed condinons. " In proixjrtion to the bulk of a species is 

 the difficulty of the conte^i wliich, as a living organized whole, 

 the individual of such species has to maintain against the 

 surroimding agencies that are ever teriding to dissolve the vital 

 bond, and subjugate the living matter to the ordinary chemical 

 and physical forces. Any changes, therefore, in such external 

 conditions as a species may have been originally adapted to exist 

 in, will militate against that existence in a degree pro])()rti()nate, 

 pe'rha])s in a geometrical ratio, to the bulk of the species. If a 

 dry season be gradually prolonged, the larne Manunal will suffer 

 from tiie drought sooner than the small one; if any alteration of 

 climate all'ect the quantity of vegetable food, the bulky Herbivore 



will first feel the effects of stinted nourishment The actual 



presence, therefore, of small species of animals in coimtries where 

 larger species of the same natural families formerly existed, is not 

 the consequence of any gradual diminution of the size of such 

 species, but is the result of circumstances which may be illus- 

 trated by the fal)le t)f the 'oak and the reed'; the smaller and 

 feebler animaK have bent, as it were, and accommodated themselves 

 to changes which have <le,str()yed the larger species." 



Moni-^ ol)>et\es. "....( )ne tendency, which has particularly 



