136 TEXT-BOOK OF ZOOLOGY 



the mother gently seizes its young offspring and conveys it into this 

 receptacle, where it finds protection, warmth and nourishment. It 

 at once presses its lips tightly to one of the nipples, and begins to 

 advance rapidly in growth. The abdominal wall of the mother is 

 supported by two so-called marsupial bones developed from the brim 

 (pubic bone) of the pelvis, by which the young is protected against the 

 pressure of the abdominal viscera of the mother. After about seven 

 months, it for the first time protrudes its head from the pouch, which it 

 now soon leaves for shorter or longer periods, but in which long after- 

 wards it seeks refuge at the approach of danger. 



Related Species. 



This mode of reproduction is proper to all other marsupials. It is 

 this which unites the numerous members of the order. For in structure 

 and mode of life the marsupials are by no means a uniform group, like 

 the rodents or apes, for example. On the contrary, they are of various 

 types, and in their characters repeat the principal forms of the whole 

 diversified class of mammals. The rodents are represented in structure 

 and mode of life by the wombat (Pliascolomys), which is about as large 

 as a spaniel, and lives in burrows like a rabbit. The marsupial weasel 

 (Da&yurus) and the marsupial wolf (Thylacinus) represent the carnivora. 

 There is also an aquatic marsupial with swimming feet, arboreal species 

 with hands and grasping feet, even a subterranean form which has been 

 aptly called the marsupial mole (Notoryctes typlilops). 



Geological discoveries prove that the marsupials in long-past ages were 

 spread over the whole earth. As, however, the structure of these animals 

 was not adapted to their mode of life in the same high degree which we 

 have seen in other mammals, it was inevitable that they should gradually 

 give place to the latter, and so vanish from the earth. In isolated 

 Australia and the neighbouring islands, however, like the egg-laying 

 monotremes, they were able to survive to the present day ; for there, as 

 there were no other mammals, they were not exposed to such a war of 

 extermination. Now, however, they are gradually giving place to the 

 mammals introduced by man (rabbits, rats, sheep, etc.). 



Also in America a few species survive the opossums, which are 

 characterized by their long, almost naked, scaly tails (Didelpltys). The 

 best-known of these is the I), rirginiana, the most notorious poultry- 

 thief of North America, whose fur is valued in Europe. 



