IXX INTRODUCTION. 



characters of classification, is much greater than in Reptiles or 

 Fishes, as will be seen in Part III. Yet there is a difference in this 

 respect in the different Orders, and the Dental System of the 

 Cetacea and Bruta has a much greater range of variation, and a less 

 constant relation to the other characters on which the families and 

 genera are founded, than in the Ungulate and higher Unguiculate 

 Species. But, with respect to these also, the value of the teeth 

 as zoological characters has been overrated. (1) 



It is true, indeed, that the most manifestly natural Mammalian 

 genera are those, the species of which are provided with absolutely 

 similar molar teeth : and, that those genera, which include species with 

 molars of different forms, do not present the same character of unity. 

 But it does not follow that, by combining species of Mammals with 

 similar molars, a group will be formed perfectly analogous to those 

 which may be considered as the most natural or perfect. Neither the 

 molar teeth, nor any other solitary character will serve to establish a 

 natural classification. 



The molar teeth will least mislead in this respect where their 

 modification is most extreme, as when they are adapted to divide the 

 flesh of animals, in which case they must of necessity be associated 

 with the faculties and instruments for seizing and destroying prey. 

 But molar teeth may be similarly modified, and equally well adapted 

 for crushing vegetable substances, which substances may be 

 sought for by one species on the dry land, by a second in 



(1) M. F. Cuvier says " Cette recherche me fit reconnaitre que tous les genres manifeste- 

 ment naturels, et admis comme tels par tous les naturalistes, etaient formes d'especes pourvues 

 de machelieres absolument semblables ; que ceux qui comprenaient des especes dent les 

 machelieres differait, n'offraient point ce caractere d'unite qui etait le partage des premieres ; et, 

 enfin, qu'en reunissant les especes a machelieres semblables on reformait des groupes parfaite- 

 raent analogues a ceux que Ton pouvait considerer comme les plus parfaits." Dents de Mam- 

 miferes, 8vo. 1825, p. ix. 



