MAMMALIA. 



303 



row in the ground (Fig. 328). An extinct wombat as 

 large as a tapir has been found in Australia. The wom- 

 bats are valued as food. Allied are the phalangers, the 

 koala that carries its young on its back (Fig. 327), and 

 many others. 



FIG. 328. Tasmanian marsupials. i, wombats ; 2, Tasmanian devil ; 3, 

 Tasmanian wolf. 



Sub-Class III. MONODELPHIA (Placental Mammals]. 



General Characteristics. In this sub-class are included 

 all the rest of the mammals. They are called placental 

 because the young, which are larger when born than the 

 preceding forms, and generally perfect, are nourished 

 up to the time of birth by a vascular membrane, pene- 

 trated by veins and arteries, known as the placenta. 



Order I. Edentata (toothless]. General Character- 

 istics. The animals of this family have no incisor teeth, 

 some being entirely toothless. In some, scales take the 

 place of hair. 



