MAMMALS 



397 



sus} of Australia and New Guinea. The egg-laying 

 habit of the duckbill may be directly traced to its 



Photograph by E. R. Sanborn, N. Y. Zoo'l. Soc. 

 FIG. 169. Echidna (Echidna aculcata). 



reptilian ancestry, but the peculiar ducklike muzzle, 

 suggesting a bird or a duck-billed dinosaur, is evidently 

 a special adaptation. The teeth are absent in the adult, 

 but present at an early stage ; so the animal has evi- 

 dently had toothed ancestors. The spiny anteaters 

 are entirely different in appearance, having strong 

 spines plentifully mixed with the fur, and the skull 

 produced into a long, slender beak, very suggestive of 

 a weevil. 



3. The Eutheria-are divided into the Marsupial and Marsupials; 

 Placental mammals. The marsupials are in some degree ga r 00 an 

 intermediate between the Prototheria and the placen- opossum, 



m, . ,. and their 



tals. The young are born in a very rudimentary con- relatives 

 dition, and are not nourished by a typical placenta or 

 base of attachment to the mother. These little-de- 

 veloped young are nearly always concealed in a pouch or 

 marsupium, where they are fed with the parent's milk. 



