THE MAMMALS 231 
Fig. 130. The duck-moles are the only mammals which 
lay eggs. One egg a year is deposited in a carefully con- 
structed nest where the young are hatched. Another order 
(#dentata) includes a number of South and Central Ameri- 
can forms, among which are the ant-eaters, armadillos, 
and tree-inhabiting sloths (Fig. 129). Still another order 
(Sirenia) includes the fish-shaped marine dugong and sea- 
cows or manatees, of which one species is found occasion- 
ally on the Florida coast. The remaining orders are de- 
scribed in the succeeding sections. 
217%. The opossums and kangaroos (Marsupialia).—The 
lowest order of mammals represented in the United States 
ew 
Fie. 131.—Opossum (Didelphys virginiana). One-tenth natural size. Photograph 
by W. H. Fisuzr. 
is that of the marsupials. It includes the opossums and 
kangaroos, together with a number of comparatively small 
and unfamiliar animals living chiefly in and about Australia. 
16 
