THE MARSUPIALS, OR POUCHED ANIMALS. 93 



to the Marsupials hence derived from common 

 primary forms their separation from these must 

 have taken place before the Trias period. 1 



2. THE MARSUPIALS, OR POUCHED ANIMALS. 



The Marsupials stand in a remarkable position 

 between the Prototheria (the Monotrema) and the 

 Eutheria (the 'higher Mammals'), but obviously 

 their relation to the latter is more direct, whereas 

 the gap between the Monotrema and the Mar- 

 supials is left to the free play of the imagination. 

 It is not readily intelligible how the marsupial 

 pouch of the Echidna which serves to protect 

 the helpless offspring could have originated by 

 natural selection. Here the two bones rising from 

 the pelvis, the ossa epipubica, transmitted to them 

 by their ancestors of the monotreme species, have 

 been brought into connection. The openings of 

 the urinary and genital organs have remained 

 at a low stage and show resemblance to the 



1 For the sake of clearness and simplicity we intend in the 

 following pages, with Huxley, to call the Monotrema, as the lowest 

 Mammal form, Prototheria. They are followed by the Marsupials 

 as Metatheria ; and all the other orders comprised as the ' higher 

 Mammalia ' then follow as Eutheria. Zoologists will know that 

 the two last designations stand for the more general terms 

 Didelphia and Monodelphia, which, however, require a special 

 explanation. 



