IV.] MIXUTE MODIFICATIONS. 125 



are those placed behind the molars having deciduous verti- 

 cal predecessors. Now, as a dentition becomes more dis- 



DEKTITION OF THE SABRE-TOOTHED TIGEB (MACHAIEODCS). 



tinctly carnivorous, so the hindmost molars and the fore- 

 most premolars disappear. In the existing cats this pro- 

 cess is carried so far that in the upper jaw only one true 

 molar is left on each side. In the machairodus there is no 

 upper true molar at all, while the premolars are reduced to 

 two, there being only these two teeth above, on each side, 

 behind the canine. 



Now, with regard to these instances of early specializa- 

 tion, as also with regard to the changed estimate of the 

 degrees of affinity between forms, it is not pretended for a 

 moment that such facts are irreconcilable with " Natural 

 Selection." Nevertheless, they point in an opposite direc- 

 tion. Of course not only is it conceivable that certain 

 antique types arrived at a high degree of specialization 

 and then disappeared ; but it is manifest they did do so. 

 Still the fact of this early degree of excessive specialization 

 tells to a certain, however small, extent against a progress 

 through excessively minute steps, whether fortuitous or 



