114 THE ORIGIN OF SPECIES 



gone on slowly changing during the accumulation of the 

 several formations and during the long intervals of time 

 between them; in this case the several formations in the 

 two regions could be arranged in the same order, in ac- 

 cordance with the general succession of the forms of life, 

 and the order would falsely appear to be strictly parallel; 

 nevertheless the species would not be all the same in the 

 apparently corresponding stages in the two regions. 



On the Affinities of Extinct Species to each other, and 



to Living Forms 



Let us now look to the mutual affinities of extinct 

 and living species. All fall into a few grand classes; 

 and this fact is at once explained on the principle of 

 descent. The more ancient any form is, the more, as a 

 general rule, it differs from living forms. But, as Buck- 

 land long ago remarked, extinct species can all be classed 

 either in still existing groups, or between them. That 

 the extinct forms of life help to fill up the intervals be- 

 tween existing genera, families, and orders, is certainly 

 true; but as this statement has often been ignored or 

 even denied, it may be well to make some remarks on 

 this subject, and to give some instances. If we confine 

 our attention either to the living or to the extinct species 

 of the same class, the series is far less perfect than if we 

 combine both into one general system. In the writings 

 of Professor Owen we continually meet with the expres- 

 sion of generalized forms, as applied to extinct animals; 

 and in the writings of Agassiz, of prophetic or synthetic 

 types; and these terms imply that such forms are in fact 

 intermediate or connecting links. Another distinguished 

 paleontologist, M. Gaudry, has shown in the most strik- 



