342 OVO-VIVIPAROUS MAMMALIA. ORDER MARSUPIALIA. 



marsupial bones, the form and position of which have been already 

 described ( 90). This order comprehends the Kangaroos, 

 Opossums, and other less known animals. The second order, 

 termed MONOTREMATA, and including only two animals at 

 present known to exist, the Ornithorhyncus, and the Echidna, 

 receives its name from a peculiarity in the structure of the 

 reproductive apparatus, which shows its near approach to the 

 class of Birds ; for the termination of the oviducts is received, 

 with that of the urinary duct, and of the intestine, into a canal 

 termed the cloaca ; so that there is but a single external orifice 

 for them both, instead of two, as in all higher animals. There 

 are many other points of structure, in which this remarkable 

 group approximates to Oviparous animals ; some of which will 

 be hereafter mentioned. 



308. The geographical distribution of this Sub-Class is not 

 one of the least curious parts of its history. With the exception 

 of the Opossum family, which inhabits America (and was the 

 first with which naturalists became acquainted), the group is 

 confined to Australia, and the nearest islands of the Indian 

 Archipelago, where not less than 70 species have been found ; 

 more probably remaining to be discovered. And with the excep- 

 tion of the Dingo Dog, a few Bats and Seals, and one or two 

 Rats, these are the only Mammalia known to exist on the vast 

 Continent of New Holland ; a circumstance which is without 

 its parallel in the distribution of the Animal Kingdom. 



ORDER XL MARSUPIALIA. 



309. From what has been just stated, of the varieties of con- 

 formation which are found in this group, it will be evidently 

 necessary to proceed at once to the description of the families into 

 which it is subdivided ; as no account can be given of their 

 general structure and habits, which shall be applicable to more 

 than a small section of the order. The first family, DIDELPHIDJE, 

 or Opossum tribe, is restricted to America, and chiefly consists of 



