192 AFFINITIES AND GEOGRAPHICAL 



transitions from class to class, which in general are the 

 leaps of the development process, the passage from reptile 

 and bird to mammal is obscure ; only indicated in a few 

 stray facts. Perhaps the fossil blank at the conclusion of the 

 cretaceous era has also helped to keep light from this subject. 

 Still we have enough to bear us out in saying, that, as the 

 fish connect with reptiles, and these with birds, so do reptiles 

 and birds together connect with mammalia ; thus placing the 

 general fact of the continued development of animal life from 

 its lowest to its highest point beyond a doubt. 



The first glimpse of the mammalian type presented by 

 geological research is in the Cetiosaur, a huge reptile of the 

 Oolite, nearly allied to the marine sauria, but exhibiting in 

 the form of the larger vertebrae a clear affinity to the whale 

 tribes. In connexion with this fact, the physiologist tells us 

 that, in the manatus and dugong, specimens of these tribes, 

 there is a dense texture of bone, and an absence of medullary 

 cavities, assimilating their skeleton to the reptiles, which 

 class they further resemble in the loose connexion of the 

 bones of the head. It would thus appear, in this grand in- 

 stance, as in all others, that the starting point of the superior 

 class was in the marine and consequently earliest examples of 

 that below ; for the trunk of the genealogical tree of Being is 

 short compared with the branches. 



The passage from the Birds to the mammalia connected 

 with them happens (for accident in the preservation of species 

 and the discovery of fossils is much concerned in the case) to 

 be more manifest. Somewhat unexpectedly but nature 

 must be taken as we find her it is the humblest mammalian 

 orders which come through this protracted channel. They are 

 the Digging Edentata (armadillos, ant-eaters, pangolins, &c.), 

 the Insectivora (moles, hedgehogs, &c.), and Rodentia (mice, 

 squirrels, hares). By all modern comparative anatomists it is 

 allowed that these show, in their osseous structure, imperfect 

 dentition, and humble character of brain, an affinity to birds. 

 There is, however, another order of animals, which can hardly 

 be considered as fully mammalian in character ; Implacental 



