Prof. Owen on Life and Species. 41 
adapted to prevailing altered conditions of the earth’s surface 
than the parental form ; and so on, until finally the extreme 
equine modifications of foot came to be ‘naturally selected,’ 
But the hypotheses of appetency and volition, as of natural se- 
lection, are less applicable, less intelligible, in connection with 
the changes in the structure and proportion of the molar series 
of teeth, which we have seen also to be gradational from Pale- 
otherium to Equus, fig. 614 
ling by the sides of the large one, like those behind the cloven 
hoof of the ox, would cause the foot of the Hipparion, e. g., 
Palzothere, to sink less deeply into swampy soil, and be more 
easily withdrawn, than the more concentratively simplified and 
specialized foot of the Horse.* : 
hinoceroses and Zebras, however, tread together the arid 
plains of Africa in the present day : and the Horse has multi- 
plied in that half of America where two or more kinds of Tapir 
still exist. That the continents of the eocene or miocene 
periods were less diversified in respect of swamp and sward, 
pampas or desert, than those of the pliocene period, has no sup- 
port from observation or analogy. 
Assuming, then, that Paleotherium did ultimately become 
Equus, I gain no conception of the operation of the effective 
force by personifying as ‘ Nature’ the aggregate of beings which 
compose the universe, or the laws which govern these beings, 
by giving to my personification an attribute which can properly 
be predicated only of intelligence, and by saying, ‘ Nature has 
selected the mid-hoof and rejected the others.’ : 
As some paragraphs in my ‘Preface’ have been miscon- 
ceived,t I must further observe, to put my meaning beyond 
doubt, that, to say that Paleotherium has graduated into 
us by ‘ Natural Selection’ is an explanation of the process 
ot the same kind and value as that which has been proffered of 
the mystery of ‘secretion.’ For example, a particular mass of 
matter ina living animal takes certain elements out of the 
blood and rejects them as ‘bile.’ Attributes were given to the 
liver which can only be predicated of the whole animal: the  —__ 
‘appetency’ of the liver, it was said, was for the elements of = 
ae 
p. 397, : Ngee 
ing to my ‘ A of Vertebrates,’ in the fqprth edition of the ‘Ori- a 
