THE EVOLUTION OF MAN 



call them, if this term were not self -contradictory, 

 are known by the scientific name of AUotheria. 

 When duckbills first became known, their bills 

 were, of course, the first thing that gave rise to 

 comment. Owing to their presence these mam- 

 mals, which otherwise had all the marks of a 

 mammal, gave a decided impression of a cross 

 with birds. For this reason some people specu- 

 lated from the beginning whether these queer 

 creatures did not actually represent the transition 

 of a mammal to a bird. In the light of the ex- 

 planation given just now, we are not very much 

 impressed with this speculation, for the bill ap- 

 pears as something unessential and subsequently 

 acquired, which has about the same significance 

 as the whalebone in the jaws of the whale, or the 

 exaggerated claws of the sloth. But the other x 

 /.characteristics of these duckbills concern us much 

 more. There is above all t 



which had not been ascertained by the first ob- 

 servers. This habit indeed indicates the descent 

 of mammals from a lower class of vertebrates. 

 But this lower class need not necessarily be birds, 

 for reptiles, amphibians and fish also lay eggs. 

 Indeed, the egg of a duckbill resembles much 

 more that of a reptile, such as a lizard, or a 

 turtle, than that of a bird. And if we consider 



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