90 THE PHYSICAL KINSHIP 



brooding pouch, periodically developed for this 

 purpose. The young of the monotremes feed on 

 the oily perspiration which exudes from the body of 

 the mother. The monotremes first appear in the 

 fossiliferous rocks of the Triassic Age. 



From the monotreme-like mammals developed 

 the marsupial mammals, animals possessing a 

 purse-like pouch on the after part of the abdomen, 

 in which they carry their young. The young of 

 marsupials are born in an extremely immature 

 state, and are carried in this pouch in order to 

 complete their development. The young of the 

 kangaroo, an animal as large as a man, are only 

 about an inch in length when they are born. 

 They are carried for nine months after their birth 

 in the marsupium of the mother, firmly attached 

 to the maternal nipple. The marsupials came 

 into existence during the Jurassic Age, and 

 during the next age, the Cretaceous, they arose 

 to considerable power. During this latter age 

 they were found on every continent. But they 

 have been almost exterminated by their more 

 powerful descendants. 



From the marsupials developed the placental 

 mammals, animals so called because their young 

 are developed within the parental body in associa- 

 tion with a peculiar nourishing organ called the 

 placenta. From the herbivorous marsupials de- 

 veloped the almost toothless edentates, the rodents, 

 or gnawing animals, the sirenians, the cetaceans, 

 and the hoofed animals, or ungulates. The 

 sirenians are fish-like animals with two flippers, 



