MONOTREMES. 



267 



MONOTREMATA. 



This order contains but few species, mostly limited to 

 Australia ; and in it we find a sort of transition from 

 mammals to birds. In fact, the shoulder of the mono- 

 tremes has the same structure as that of birds and rep- 

 tiles ; their urinary system is like that of birds, and their 

 teeth are either shed early in life or entirely absent. 

 There are no mammae, the mammary glands opening 

 directly on the surface of the skin ; and the female lays 



FIG. 208. 



ORNITHGRHYNCHUS PARADOXTJS. 



eggs, from which the young are hatched, thus differing 

 from all other mammals. 



The ornithorhynchus is the most interesting of this 

 order. By the Australian colonists it is called water- 

 mole. Its teeth drop out before it reaches adult life, 

 leaving on each side of the jaw two horny prominences, 

 which serve the purposes of mastication in the adult. 

 The mouth is surrounded with naked skin, which forms 

 folds at its base, and looks much like the bill of a duck. 

 The length is eighteen to twenty inches from tip to tip, 

 and the body is covered with short, soft fur. The animal 



