ORDERS OP THE CLASS MAMMALIA. 77 



which establish a communication between the em- 

 bryo and the mother, from whom the former receives 

 its nourishment, and in all probability its oxygena- 

 tion. The fetuses have also, at least in the earlier 

 periods of gestation, a vesicle analogous to that 

 which contains the yolk in the oviparous kinds, and 

 receiving supplies in the same manner from the 

 vessels of the mesentery. They have also another 

 bladder corresponding to that of the urine, which 

 has received the name of allantoic. $ 



The young are nourished for some time after 

 their birth, by the milk, a liquor peculiar to this 

 class, which is produced at the very moment of 

 parturition, and for as long after as is requisite for 

 the nutriment of the young. It is from the mammae 

 or teats that this class is named, this being a cha- 

 racteristic exclusively peculiar to themselves, and 

 consequently fitter than any other external one for 

 the purposes of distinction. 



Division of the Class Mammalia into orders. 



The most essential differences of the mammalia 

 among themselves are, first, in the organs of touch, 

 on which the dexterity of the animal mainly de- 

 pends ; and secondly, in those of mastication, 

 which determine the nature of the aliment proper 

 to every species. On these essential characters 

 are founded the division of the mammalia into 

 orders. 



Every thing relating to the digestive functions is 



