598 THE REPRODUCTIVE FUNCTIONS. 



tribes, again, which, according to circumstances, 

 are either oviparous, or ovo-viviparous : this is 

 the case with the Shark. 



3. Viviparous animals are those in which no 

 egg, properly so called, is completed ; but the 

 ovum, after proceeding through the oviduct, 

 sends out vessels, which form an attachment to 

 the interior of a cavity in the body of the parent, 

 whence it draws nourishment, and therefore has 

 attained a considerable size at the time of its 

 birth. 



4. Marsupial animals are those, which, like 

 the KanguroOy and the Opossum, are provided 

 with abdominal pouches, into which the young, 

 born at a very early stage of developement, are 

 received, and nourished with milk, secreted from 

 glands contained within these pouches. As the 

 young, both in this and in the last case, are nou- 

 rished with milk prepared by similar glands, or 

 MammcB, the whole class of viviparous and mar- 

 supial animals has received, from this charac- 

 teristic circumstance, the name of Mammalia. 



