﻿194 Allen's naturalist's library. 



moderately-sized blind appendage, or caecum. Pouch generally 

 wanting, sometimes composed merely of two lateral folds of 

 skin not united at the ends, and rarely complete. Three pairs 

 of premolar teeth, the last of which always has a well-developed 

 deciduous predecessor. 



The Opossums, which include more than a score of species, 

 varying in size from that of a Cat to that of a Mouse, are con- 

 fined at the present day to America, where they range from 

 the United States to Argentina. They may, however, be re- 

 garded as more especially characteristic of the wooded districts 

 of the southern half of that continent, but during the early part 

 of the Tertiary period their range included England and other 

 parts of Europe. Very similar to one another in external 

 appearance, as well as in internal structure, the whole of the 

 species, with the exception of a single one di-stinguished by its 

 webbed feet and aquatic habits, are included in one large 

 genus, which, however, may be split up into several subgenerie 

 groups, thus rendering it less unwieldy than would other- 

 wise be the case. As a whole, the family is regarded by 

 Mr. Thomas as very closely allied to the Dasyuridce ; one of 

 its main claims to distinction being its isolated geographical 

 distribution. 



The Opossums being among the lowest of Marsupials, the 

 existence of a complete pouch among certain species is of the 

 greatest importance as showing that this organ is primitively an 

 essential characteristic of Marsupials, and not one that has 

 been specially developed to suit the exigencies of the various 

 modes of life of the Australian members of the order. Con- 

 sequently those forms, like the majority of the Opossums and 

 the Banded Ant-eaters, which have either no pouch or merely a 

 rudiment thereof, may be safely assumed to have lost thnt 

 organ through specialisation. The reason of the loss of such 

 an organ, which appears so admirably adapted for the protec- 



