THE PHYLA HEMICHORDATA AND CHORDATA 



Fig. 18.31. Representative Metatheria or 

 Marsupialia. A, rock wallaby, Wallabia 

 bicolor, with young in marsupium. B, koala, 

 Phascolardos cimreus, with young. C and D, 

 Virginia opossum, Didelphys viramiana, with 

 young. In C, the young can be seen within 

 the marsupium of the mother. {A and B, 

 photographs courtesy New York Zoological 

 Society; C and D, photographs by Charles 

 W. Schwartz.) 



