PREFACE. xxix 



Cuvier, * whether I should have ever divined, if observation had 

 not taught it me, that the ruminant hoofed beasts should all have 

 the cloven-foot, and be the only beasts with horns on the frontal 

 bone.' l I may add that we know as little why horns should be in 

 one or two pairs in those ungulates only which have hoofs in one 

 or two pairs ; whilst in the horned ungulates with three hoofs 

 there should be either one horn, or two odd horns placed one be- 

 hind the other, in the middle line of the skull ; or why the ungu- 

 lates with one or three hoofs on the hind foot should have three 

 trochanters on the femur, whilst those with two or four hoofs on 

 the hind foot should have only two trochanters. 2 



' However,' continues Cuvier, ' since these relations are con- 

 stant, they must have a sufficing cause ; but as we are ignorant 

 of it, we must supply the want of the theory by means of observa- 

 tion. This will serve to establish empirical laws if adequately 

 pursued, as sure in their application as rational ones.' 3 'That 

 there are secret reasons for all these relations observation may 

 convince us, independently of general philosophy.' ' The con- 

 stancy between such a form of such organ and such another form 

 of another organ is not merely specific, but one of class with a 

 corresponding gradation in the development of the two organs.' 4 



1 For example, the dentary system of non-ruminant ungulates 

 is generally more perfect than that of the bisulcates ; inasmuch 

 as the former have almost always both incisors and canines in the 

 upper as well as the lower jaw ; the structure of their feet is in 

 general more complex, inasmuch as they have more digits or hoofs 

 less completely enveloping the phalanges, or more bones distinct 



1 Op. cit. 50. 2 Quarterly Journal of the Geological Society, p. 138. 1847. 



3 ' Puisque ces rapports sont constants, il faut bien qu'ils aient une cause suffisante, 

 mais corame nous ne la connaissons pas, nous devons supplier au defaut de la theorie 

 par le moyen de 1' observation.' — Op. cit. p. 50. 



4 ' En effet, quand on forme un tableau de ces rapports, on y remarque non seulement 

 une consistance specifique, si Ton peut s'exprimer ainsi, entre telle forme de tel organe 

 et telle autre forme d'un organ different ; mais Ton aper<joit aussi une Constance 

 classique et une gradation correspondante dans le developpement de ces deux organes, 

 qui montrent, presque aussi bien qu'un raisonnement effectif, leur influence mutuelle.' — 

 Op. cit, p. 51. 



