GENERAL CONCLUSIONS. 793 



than in Palceotherium and Anoplotherium, affording additional 

 significant evidence of progressive departure from generalised 

 type. Thus, the succession in time accords with the gradational 

 modifications by which Pal&otherium is linked on to Equus. 



With this additional knowledge the question, ' whether actual 

 races may not be modifications of those ancient races which are 

 exemplified by fossil remains ?' presents itself under very different 

 conditions from those under which it passed before the minds of 

 Cuvier 1 and the Academicians of 1830. If the alternative — 

 species by miracle or by law ? — -be applied to Palceotherium, Pa- 

 loplotherium, Anchitherium, Hipparion, Equus, I accept the latter, 

 without misgiving, and recognise such law as continuously ope- 

 rative throughout tertiary time. 



In respect to its mode of operation, we may suppose Lamarck 

 to say, ' as the surface of the earth consolidated, the larger and 

 more produced mid-hoof of the old three-toed Pachyderms took a 

 greater share in sustaining the animal's weight ; and, more blood 

 being required to meet the greater demand of the more active 

 middle-toe, it grew; whilst the side-toes, losing their share of 

 nourishment and becoming more and more withdrawn from use, 

 shrank ; ' and so on, according to the hardening of the ground, 

 until only the hidden rudiments of metapodials remained and one 

 hoof became maximised for all the work. Mr. Darwin, I con- 

 ceive, would modify this, like other Lamarckian instances, by 

 saying that some individuals of Palceotherium happening to be 

 born with a larger and longer middle-toe, and with shorter and 

 smaller side-toes, such variety was better 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 appe- 

 tency and volition, as of natural selection, 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 Palceotherium to Equus, fig. 

 614. 



Any modification of Geoffroy's ' ambient medium,' affecting the 

 density of the soil might so far relate to the changes of limb- 

 structure, as that a foot with a pair of small hoofs dangling 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., and a fortiori 

 the broader based three-hoofed foot of the Palaeothere, to sink 

 less deeply into swampy soil, and be more easily withdrawn, than 



1 ' Pourquoi les races actuelles, me dirait-on, ne seraient-elles pas des modifications 

 de ces races ancieimes que Ton trouve parmi les fossiles ? ' — cxxxix. i. p. lvii. 



