138 



Biology in America 



ourselves "up a stump," is to accept the philosophy of Topsy 

 and admit that they "jest grew." 



Tlie ]\Iesozoic and early Eocene mammals were all primi- 

 tive types and most of them disappeared from the face of the 

 earth without leaving any descendants. 



"It is the mammals which were the strangest element of 

 Paleoccne life, and (an) imaginary observer would find no 

 creature tliat he had ever seen before. The difference from 

 modern mammalian life was not merely one of species, genera 

 or even families, but of orders, for only one, or at most two, 



The Opossum 



The only marsupial at j)reseiit found in the United States. 



Photo hij Elu-iih /'. Sa)iJ)orn. 



By permission of the Neic York Zoological Society. 



of the orders now living were then to be found in North 

 America, and both of these (marsupials and insectivores) were 

 primitive and archaic groups, which seem like belated sur- 

 vivals in the modern world." ^ 



It is possible however that the marsupial types of these 

 early mammals have come down to us as the marsupials of 

 the present. The marsupials derive their name from the 

 marsupium or pouch in which they carry the young for some 

 time after birth. These latter are born in a very undevel- 

 oped condition and at birth are transferred by the mother 



'Scott, "History of Land Mammals in the Western Hemisphere," p. 

 284. By permission of the Macmillan Company. 



