XIV FUNDAMENTAL PROBLEMS 423 



become useful, as in the case of the single enlarged claw of 

 many Crustacea, it has been preserved by natural selection. 



Origin of the Feet of the Ungulates. 



Perhaps the most original and suggestive of IVIr. Cope's 

 applications of the theory of use and effort in modifying 

 structure are, his chapters "On the Origin of the Foot-Structure 

 of the Ungulates ; " and that " On the Eflect of Impacts and 

 Strains on'the Feet of Mammalia ; " and they will serve also 

 to show the comparative merits of this theory and that of 

 natui'al selection in explaining a difficult case of modification, 

 especially as it is an explanation claimed as new and 

 original when first enunciated in 188L Let us, then, see 

 how he deals with the problem. 



The remarkable progressive change of a four or five-toed 

 ancestor into the one-toed horse, and the equally remarkable 

 division of the whole group of ungulate animals into the odd- 

 toed and even-toed divisions, Mr. Cope attempts to explain 

 by the effects of impact and use among animals which 

 frequented hard or swampy ground respectively. On hard 

 ground, it is urged, the long middle toe would be most 

 used and subjected to the greatest strains, and would 

 therefore acquire both strength and development. It would 

 then be still more exclusively used, and the extra nourish- 

 ment required by it would be drawn from the adjacent less- 

 used toes, which would accordingly diminish in size, till, after 

 a long series of changes, the records of which are so well 

 preserved in the American tertiary rocks, the true one-toed 

 horse was developed. In soft or swampy ground, on the other 

 hand, the tendency would be to spread out the foot so that 

 there were two toes on each side. The two middle toes 

 would thus be most used and most subject to strains, and 

 would, therefore, increase at the expense of the lateral toes. 

 There would be, no doubt, an advantage in these two func- 

 tional toes being of equal size, so as to prevent twisting of the 

 foot while walking ; and variations tending to bring this about 

 would be advantageous, and would therefore be preserved. 

 Thus, by a parallel series of changes in another direction, 

 adapted to a distinct set of conditions, we should arrive at the 

 symmetrical divided hoofs of our deer and cattle. The fact 



