CHAPTER XXIV. 



THE COMMON OPOSSUM AND ITS KIN. 



(Didelpliys virginiana.) 



HE Common Opossum stands the lowest in point of de- 

 velopment of all the members representing the mam- 

 malian fauna of the United States; therefore in any 

 list of mammals of this country, presented in linear se- 

 ries, the Opossums are given first, in order to indicate this fact. 

 Belonging, however, as they do to the marsupial group of ani- 

 mals, the opossums are in another sense the most typically mam- 

 malian of all the class Mammalia. The reason assigned for this 

 is, that in them respiration, as performed by the lungs, and the 

 maternal secretion of milk appear earlier and thus antedate all 

 other modes in supplying the requisite amount of oxygen and 

 nutriment for the development of the young. As in other mar- 

 supials the presence of the mammary glands in this group, and 

 the healthy operation of their milk-secreting function is abso- 

 lutely essential to the perpetuation of the species. Taken as an 

 order the marsupial animals are confined to the American con- 

 tinent and to the Australian region, and although in their exter- 

 nal forms and internal structure they exhibit very notable di- 

 versity, yet for the sake of convenience naturalists continue to 

 thus group them as the Marsupialia. As thus restricted they 

 constitute the subclass (of the class Mammalia) termed the Meta- 

 theria or DidelpMa. 



Opossums, or the family Didelpliidce, are peculiar to the conti- 

 nent of America, not now being found in any other part of the 

 world, though they there formerly existed, as fossil remains of 

 them have been found in the Eocene and early Miocene periods 

 of Europe. 



Mr. Oldfield Thomas, of the British Museum, a great author- 

 ity upon mammals, says of the existing forms that " opossums 

 are small animals, varying from the size of a mouse to that of a 

 large cat, with long noses, ears, and tails, the latter being, as a 

 rule, naked and prehensile, and with great toes so fully oppos- 

 able to the other digits as to constitute a functionally perfect 

 posterior pair of ' hands. 7 These opposable great toes are with- 

 out nail or claw, but their tips are expanded into broad, flat pads. 



