THE NOTOG^IC REALM. 



[CHAP. 



The egg-laying mammals, or monotremes, constitute not only 

 a distinct order (Monotremata), but likewise a 



Monotremes. . N 



separate sub-class (Prototheria); and are broadly 

 distinguished from all other members of their class by laying eggs, 

 from which the young are in due course hatched; as they are likewise 

 by the milk-glands of the female opening on the surface of the 

 skin by means of a number of minute perforations, without being 

 furnished with nipples. The group is represented by three genera, 



FIG. i. THE DUCKBILL. (Ornithorhynchus anatinus.} 



one of which is widely different from the other two and forms a 

 family by itself, while the latter constitute a second family. The 

 duckbill {Ornithorhynchus anatinus}, as the single representative 

 of the first family (OrnithorhynchidcB) is commonly termed, is an 

 aquatic, somewhat mole-like, burrowing animal, easily recognised 

 by the expansion of the muzzle into a broad duck-like beak 

 covered during life with a sensitive skin, and also by the broadly 

 webbed feet, of which the soles are naked and devoid of pads. 



