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vegetables which could be masticated by teeth wholly destitute of enamel, and 

 chiefly composed of caementum or bony crust, and of a substance softer than 

 bone, viz. coarse dentine everywhere drilled by numerous and close-set vascular 

 canals, must necessarily have been of the softer kind, as bulbs and cellular 

 and amylaceous tubers. Such roots, as produced in a state of nature, yield 

 sustenance at the present day to the smaller-sized quadrupeds only, and of these 

 the purely rhizophagous species are very few in number. The history of plants 

 reveals no natural conditions under which nutritious bulbs or tubers are deve- 

 loped so abundantly, diffused so extensively, or reproduced so rapidly, as to have 

 afforded the daily food of the Megatheriums, Mylodons, Megalonyxes, Scelido- 

 theriums, &c., which seem to have coexisted in not sparing numbers in the 

 primaeval wilds of the American continents. To support by such food the smaller 

 domestic quadrupeds during a part of the year demands much toil and the highest 

 art of husbandry in order to produce the requisite field-crops. The assumption 

 of a like fertility in nature, as a peculiarity of an early and golden period of the 

 earth's history, seems not less arbitrary than the supposition that the trees of 

 the same period towered aloft under such gigantic proportions as to have sus- 

 tained Megatheriums suspended from their boughs by prehensile tails as easilv 

 and securely as the assumed dwarfish successors to such hypothetical trees now 

 support the puny Sloths. According to the known natural rate of growth of 

 such tubers and bulbs as the teeth of the Megatherioids could have crushed, 

 much ground must have been devastated and ploughed up in the quest of as 

 many as might serve for one day's subsistence ; but, according to the theory ad- 

 vocated in the present Memoir, the Megatherium or Mylodon would have abun- 

 dance of food for several days in the branches of a tree large enough to have 

 tasked its powers in the prostration. 



I have next to remark that the observed varieties in the teeth of theMegathe- 

 rioid animals are best explained, teleologically, on the theory that they fed on 

 foliage. The close correspondence between the Megatherium and the Mylodon 

 in the modifications of the skeleton determining the peculiar forces acting from 

 the hind upon the fore-parts, compels us to infer that they resembled each other 

 in the mode in which they obtained their sustenance ; and, nevertheless, the 

 difference in the form of the grinding surface of the teeth, as well as in their size 

 and depth of insertion, obviously indicates some difference in the substances com- 



