40 Prof. Owen on Life and Species. 
genera to have co-existed. One cannot doubt, also, that every 
well-marked species of these genera paired within itself, and — 
that they exemplified respectively the character of a ‘group of — 
individuals descended from common parents, or from such as ~ 
resembled them as closely as they resembled each other.’ They 7 
did not, however, exist as species, during the same periods of | 
time, far less so ‘from the beginning of things.’ The single- — 
hooted Horse-family cannot be traced further back than the 
pliocene tertiary period: the tridactyle equine species have not 
been found in strata earlier than miocene, and disappear in the — 
upper eocene: the heavier-bodied shorter-legged species with 7 
three functional hoofs to each foot belong to upper and middle 
eocenes. T'urthermore, in the oldest eocene (London clay, | 
super-cretaceous Conglomerates and Plastic clay at Meudon, | 
Paris,) we get evidence of Ungulates (Pliolophus, Hyracothe- | 
rium, Coryphodon,) in which the perisso- and artio-dactyle char- | 
acters were less differentiated than in Paleotherium and Ano- ~ 
plotherium, affording additional significant evidence of progres- | 
sive departure from generalized type. us, the succession in | 
time accords with the gradational modifications by which Pale- — 
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* and the Academicians of 1830. If the 
alternatiye—species by miracle or by law ?—be applied to 
Paleotherium, Paloplotherium, Anchitherium, Hipparion, 
quus, Laccept the latter, without misgiving, and recognize 
such law as continuously operative throughout tertiary time. 
In respect to its mode of operation, we may suppose Lamarck 
ing of the ground, until 
dials remained and one hoof. 
Mr. nue 
ian instances, by saying that some individuals of Paleothe- 
be born with a larger and longer middle-toe, 
smaller side-toes, such variety was better 
de ces races anciennes que l’on trouve parmi les fossiles ?—oxxarx, i, p. lit 
