Chap. XL] AFFINITIES OF EXTINCT SPECIES. 107 



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

 a general rule, it differs from living forms. But, as 

 Buckland 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 between 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 con- 

 tinually meet with the expression of generalised 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 striking manner that 

 many of the fossil mammals discovered by him in Attica 

 serve to break down the intervals between existing 

 genera. Cuvier ranked the Euminants and Pachyderms, 

 as two of the most distinct orders of mammals : but so 

 many fossil links have been disentombed that Owen 

 has had to alter the whole classification, and has placed 

 certain pachyderms in the same sub-order with rumi- 

 nants ; for example, he dissolves, by gradations the 

 apparently wide interval between the pig and the 

 camel. The Ungulata or hoofed quadrupeds are now 

 divided into the even-toed or odd-toed divisions ; but 

 the Macrauchenia of S. America connects to a certain 

 extent these two grand divisions. No one will deny 

 that the Hipparion is intermediate between the existing 



