268 The Study of Animal Life part iii 



tional. The brain of mammals is more highly developed than 

 that of other animals, and in the great majority there is a prolonged 

 (placental) connection between the unborn young and the mother. 

 In all cases the mothers feed the tender young with milk. 



In the class there are three grades : — 



(i) In the Duckmole (Ornithorhynchus) and the Porcupine 

 Ant-Eater {Echidna), and perhaps another genus Proeckidna, the 

 females lay eggs. In many other ways these exclusively Austral- 

 asian mammals are primitive, exhibiting affinities with reptiles. 



(2) In the Marsupials, which, with the exception of some 

 American Opossums, are also Australasian, the young are born at 

 a very tender age, as it were, prematurely. In the great majority 

 of genera, the mothers stow them away in an external pouch, where 

 they are fed and sheltered till able to fend for themselves. In ' 

 Australia the Marsupials have been saved by insulation from stronger 

 mammals, which seem to have exterminated them in other parts 

 of the earth, the Opossums which hide in American forests being 

 the only Marsupials surviving outside Australasia, though fossils 

 show that the race had once a much wider distribution. In their 

 Australian retreat, apart from all higher Mammalia (mice, rabbits, 

 and the like being modern imports) the Marsupials have evolved 

 along many lines, prophetic of the higher orders of mammals. 

 There are ' ' carnivores " like the Thylacine and the Dasyure, 

 " herbivores " like the Kangaroos, " insectivores " like the banded 

 ant-eater Myrmecobius, and "rodents" like the Wombat. 



(3) In all the other orders of mammals there is a close con- 

 nection between mother and unborn offspring. 



Two orders are lowly and distinctly separate from the others 

 and from one another — the Edentata represented by sloths, 

 ant-eaters, armadillos, pangolins, and the Aard-Vark ; and the 

 Sirenia or Sea-Cows which now include only the dugong and the 

 manatee. 



Along one fairly definite line we may rank three other orders 

 — the Insectivores, the Bats, and the Carnivores. The hedgehog, 

 which is at once a lowly and a. central type of mammal, 'may be 

 taken as the beginning of this line. Along with shrews, moles, 

 porcupines, the hedgehogs form the order Insectivora. To these 

 the Bats (Cheiroptera), with their bird-like powers of flight, are 

 linked, while the Carnivora (cats, dogs, bears, and seals), though 

 progressive in a different direction, seem also related. 



Comparable to the Insectivores, but on a different line, are the 

 gnawing Rodents, rabbits and hares, rats and mice, squirrels and 

 beavers. This line leads on to the Elephants, from the company 

 of which the mammoths have disappeared since man arose on the 

 earth. With the Elephants, the rock-coneys or Hyraxes — ' ' a feeble 



