THE ALLIES OF THE SQUIRREL: MAMMALIA 411 



The Australian fauna evolved along various lines, produ- 

 cing herbivorous, insectivorous, and carnivorous forms which 

 resemble in outward appearance the members of the higher 

 orders, though they are in reality marsupial in structure. 

 Over, the rest of the world, witli the exception of America, 

 the marsupials were entirely destroyed and their places taken 

 by more highly specialized types. Marsupials retained a foot- 

 hold in South America owing to the absence of overpowering 

 enemies, and on account of their adaptation to climatic and 



FIG. 217. Photograph of Armadillo 



general environmental conditions. They afford an illustration 

 of discontinuous distribution. 



Sloths, Armadillos, and Allies. Both terrestrial and arboreal 

 animals are included in the order Edenta'ta (Lat. e, out; dens, 

 tooth). Edentates have incompletely developed teeth, or if 

 the teeth are well developed, they are of simple structure; 

 true incisors are never present. Many members of the order 

 have a covering of scales formed from the hardening of the 

 skin. 



The armadillos (Fig. 217) are terrestrial American forms 

 which are protected by the scaly covering just referred to. 

 The tail and head are generally exposed, but the animals can 



