MAMMALS. 



575 



ducks there were ridges which served to strain the water from the food, 

 and in this animal exactly the same structure is seen — four horny teeth, 

 which evidently subserve a similar purpose ; true teeth occurring only in 

 early life. 



Fig. 474. — Skeleton of the duck-bill. 



The duck-mole (another of its names) lives an aquatic and a burrowing 

 life. A little above the water are seen the entrances of the serpentine 

 burrows, which go obliquely upwards and terminate in a large chamber, 

 where the nest of grass and dried leaves is placed. In hunting for their 

 food they paddle along, with the head beneath the water like a duck., 

 turning over the sand and stones, and sifting out the insects and crusta- 

 ceans which abound in such localities. 

 These are stored in pouches in the 

 cheeks, and then, after the fishing is 

 over, they are crushed and ground be- 

 tween the horny teeth. The web of the 

 foot, so useful in swimming, would be 

 in the way while digging or traveling 

 through the burrows, and so it folds 

 over on the sole of the foot when the 

 animals leave the water. 



The echidnas, or porcupine ant-eat- 

 ers, are much different in their ex- 

 ternal appearance. The duck-like bill 

 and webbed feet are lacking, while the 

 mouth is but a small orifice at the end of the snout, merely large enough 

 to allow the tongue to pass in and out. Then, too, the fur is different ; 

 for among the hair are spines two or three inches long, which are much 

 like those of the more familiar porcupines. As this difference in struc- 

 ture would indicate, there is a great difference in their habits ; for the 

 latter animal is a terrestrial species, which burrows in the earth in the 

 search for ants, which form its food. When a nest is found, the animal 

 sticks out its long tongue covered with an adhesive saliva, and then draws 

 it in covered with ants. 



Fig. 475. — The duck-bill (Ornithorhynchus para- 

 doxus). 



