378 ORIGIN OF SPECIES 



fers from living forms. But, as Buckland long ago re- 

 marked, extinct species can all be classed either in still ex- 

 isting 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 in- 

 stances. If we confine our attention either to the living or 

 to the extinct species of the same class, the series is far less 

 perfect that if we combine both into one general system. In 

 the writings of Professor Owen we continually meet with 

 the expression of generalised forms, as applied to extinct 

 animals; and in the writings of Agassiz, of prophetic or syn- 

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

 fact intermediate or connecting links. Another distinguished 

 palaeontologist, 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 Ruminants 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 pachy- 

 derms 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 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 horse 

 and certain older ungulate forms. What a wonderful con- 

 necting link in the chain of mammals is the Typotherium 

 from S. America, as the name given to it by Professor Ger- 

 vais expresses, and which cannot be placed in any existing 

 order. The Sirenia form a very distinct group of mammals, 

 and one of the most remarkable peculiarities in the existing 

 dugong and lamentin is the entire absence of hind limbs 

 without even a rudiment being left; but the extinct Hali- 

 therium had, according to Professor Flower, an ossified 

 thigh-bone "articulated to a well-defined acetabulum in the 

 pelvis," and it thus makes some approach to ordinary hoofed 



