Chap. XI.] 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 in- 

 tervals 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 sys- 

 tem. In the writings of Professor Owen we continu- 

 ally 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 palffibntolo- 

 gist, 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 exist- 

 ing genera. Cuvier ranked the Ruminants and Pachy- 

 derms 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 

 ruminants; 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 Mac- 

 rauchenia of S. America connects to a certain extent 

 these two grand divisions. No one will deny that the 

 Hipparion is intermediate between the existing horse 



