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 Mr. 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 Effect 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 
natural selection in explaining a difficult case of modification, 
especially as it is an explanation claimed as new and 
original when first enunciated in 1881 . Let us, then, see 
how he deals with the problem. 
The remarkable progressive change of a four or live-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 
