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PREFACE. 



There is, perhaps, no branch of Biology which in recent years has 

 advanced so rapidly, and, on the whole, so surely and in so many 

 directions, as has Palaeontology. In the earlier periods of its devel- 

 opment, a tendency has, indeed, been sometimes shown by investi- 

 gators concerned exclusively with existing forms of life to depreciate 

 the position of Palaeontology as a Science, and to contest its claims 

 to recognition as a separate department of Zoology and Botany ■ nor 

 can it be said that this tendency has yet altogether died out. Even 

 now, it is sometimes considered that Palaeontology, on the ground 

 of its relation to the chronological history of the earth, should be 

 regarded as a branch of Geology, rather than of Biology ; while on 

 the ground of its being necessarily concerned almost wholly with 

 the skeletal structures of aninials and plants, its conclusions have 

 been discredited, and the adequacy of its methods of investigation 

 has been questioned. 



No one, however, who has made himself thoroughly acquainted 

 with the progress of this branch of investigation during the last 

 decade, can doubt that Palaeontology has amply vindicated its claim 

 to be regarded as a special department of Biology, as entirely sci- 

 entific in its character and methods, and in all respects as worthy 

 of separate and special study as is, for example, the department of 

 Embryology. 



So numerous and so extensive have been the advances made by 

 Palaeontology of late years, that the Authors have found it necessary 

 not only to largely increase the bulk of the present, as compared 

 with the last, edition of this work ; but also to entirely recast and 

 rewrite it, while the illustrations to the text have been nearly 



