THE LAWS OF EVOLUTION EMPHASIZED. 361 



True Carnivores appeared in the newer Eocene, Chei- 

 roptera in the middle Eocene, and true Primates in the older 

 Miocene. 



In these orders of placental mammals 56 genera appeared 

 for the first time in the older Eocene, and there were succes- 

 sively added to them, in the middle Eocene 40 new genera, 

 in the newer Eocene 105 new genera, Oligocene 5, older Mio- 

 cene 49, newer Miocene 34, Pliocene 27; or previous to the 

 opening of the Pleistocene 260 genera, distributed among the 

 seven land orders of mammals, of which the first traces were 

 obtained from the older Eocene beds of North America and 

 Europe. The Australian, South American, and African types 

 are not here included ; and it must be remembered also that 

 new discoveries are constantly adding to these statistics, and 

 in general they augment the earlier more than the later totals. 



Again, the fact that (? Prototheria and) Metatheria were 

 already well developed in genera in the Mesozoic does not 

 lessen the significance of the remarkable expansion of the 

 mammals in the older Eocene period ; nor does the imperfec- 

 tion of knowledge lessen the testimony to the relatively- 

 sudden expansion which the evidence now in hand indicates. 

 The approach to recent time, and the increasingly better rep- 

 resentation of the land faunas among the preserved remains, 

 does not invalidate the truth of the general proposition, that 

 all the grand features of structural modification, expressed in 

 the subclass of placental mammals, made their appearance in 

 distinct genera with great rapidity at the first stage of ap- 

 pearance of the Placentalia. 



The prominent differences, expressed in the limbs, teeth, 

 form, and habits, in the hoofed animals, the odd and even 

 toes, the gnawing rodents, the flesh-eating Carnivores (Creo- 

 donts), the insect-eaters, the flying bats, and the climbing 

 monkeys, were all seen among the members of the first fauna 

 of the new type of placental mammals, in the Eocene period. 



Synthetic Types Illustrated by the Vertebrates of the Mesozoic. 

 No better illustration of the principle of the " synthetic" 

 or " comprehensive" character of early types of organization 

 is to be found than that presented by the Dinosaurian rep- 

 tiles and the reptilian birds of the Mesozoic. Here we find 



