372 TYPES OF ANIMAL LIFE 



It is difficult, if not impossible, to believe that the 

 armadillos, pangolins, and aard-vark ever had any 

 common ancestors, save such as were near the base of 

 the whole mammalian tree of life. The whales and 

 porpoises on the one hand, and the sirenia (or mer- 

 maids) on the other, are both isolated groups ; though we 

 may in imagination connect the latter with the elephant 

 and odd-toed ungulates, and the former with the non- 

 ruminating, even-toed, hoofed beasts. 



The rodents are also isolated, but that their peculiar 

 kind of dentition has more than once arisen independently 

 is proved to us by the wombat and the aye-aye, both of 

 which, though no rodents, have rodent-Hke cutting teeth. 



The seals and sea-bears or pinnipedia are doubtless 

 modified carnivora of one kind or another, and the car- 

 nivora themselves may have been modified from early 

 insectivora. The origin of lemuroids is, as recently 

 stated, problematical, while as to that of bats we have 

 as yet no fragment of evidence. 



Monkeys, as we pointed out in our first article, stand 

 alone on a veritable zoological island, save that the human 

 form very closely resembles them. 



As to the origin of the whole class Mammalia, we 

 have not yet enough evidence to enable us to affirm 

 anything with certainty, but probability points to its 

 derivation from one or other of the earlier forms of 

 reptilian life. 



It now remains but to glance over the earth's surface 

 and see what are the beasts which characterise, respect- 

 ively, its several geographical regions. The first region, 

 which is made up by Europe, Africa north of the Sahara, 

 and Asia north of the Himalaya — excluding the south 

 of Arabia — may be called the Northern Old World region. 

 This is the special region of sheep, and goats, and deer. 



