﻿MARSUPIALS IN GENERAL. 9 



forced injection of milk from the mammary glands. This is 

 brought about by the upper part of the larynx, or extremity of 

 the wind-pipe, being at this period of existence so much 

 elongated as to project through the fauces or hinder aperture 

 of the mouth and reach the internal nostrils. By this means 

 a closed passage is formed from the nostrils to the lungs, and 

 the young creature can thus breathe securely while a stream 

 of milk is flowing down its mouth and throat into the 

 stomach. It is noteworthy that this condition, which is 

 merely transitory among the Marsupials, persists throughout 

 life in the Cetaceans. 



The whole of the animals presenting the foregoing charac- 

 teristics constitute one Order, to which zoologists apply the 

 name of Marsupialia. The differences by which the Marsu- 

 pialia are distinguished from the higher orders of Mammalia 

 are, however, so much greater than those by which the latter 

 are severally differentiated from one another, that it has been 

 further considered advisable to regard the whole of the latter 

 as constituting one great Sub-class, while the Marsupials form 

 a second Sub-class to themselves. For the Sub-class compris- 

 ing all the higher Mammals naturalists have adopted the names 

 of Monodelphia, Placentalia, or Eutheria ; while for the one re- 

 presented solely by the Marsupialia, the names of Didelphia, 

 Implacentalia, and Metatheria have been proposed. 



So different in general form and appearance from one 

 another are many of the Marsupials — some, like the Thylacine, 

 being carnivores, adapted for walking, while others, like the 

 Kangaroos, are herbivorous, with limbs suited for leaping — 

 that it might at first sight appear that the Sub-class Didelphia 

 might well be subdivided into distinct orders, in the same 

 manner as the Monodelphia or Eutheria are split up into the 

 Primates, Carnivora, Rodentia, Ungulata, &c. It has been 

 found, however, that structurally all the Marsupials are so 



