66 EVOLUTION OF TO-DAY. 



But although this is true, fossils do enable the 

 naturalist to classify all divisions within the sub- 

 kingdoms, in a tree-like arrangement, by presenting 

 numerous links. To consider briefly an example. 

 The vertebrates to-day consist of many widely separ- 

 ated orders unconnected by intermediate forms. 

 But fossil vertebrates are very numerous, and in a 

 great many cases fall into gaps between existing 

 orders. The Ungulates, the Proboscidea, the Hyra- 

 coidea, and the Sirenia, can all be traced backwards 

 by converging lines, until they meet at a point rep- 

 resented by a mammal of the lower tertiary. The 

 Cetacea, Carnivora, and Rodents in like manner 

 approach each other. The birds and reptiles ap- 

 proach ancient Cretaceous forms, which represent 

 their common point of origin, although the record 

 is less perfect here than in the case of mammals. 

 Beyond the Cretaceous the record is so incomplete 

 as to make the history less positive : but the evi- 

 dence, as far as collected, points to the union of all 

 the classes of vertebrates in some ancient fish-like 

 form which lived in the Silurian age. In no case is 

 the record of these lines complete ; even in the 

 most perfect instances there are many gaps. But 

 fossils do show many of the intermediate links for 

 which we are searching, and beyond a shadow of 

 doubt the paleontological record indicates that the 

 classification of the animals within any given sub- 

 kingdom is such as is represented by the tree-like 

 arrangement of expressing relations. 



In order to complete the evidence that this repre- 

 sents the true classification of the whole animal 



