CHAPTEE XL 

 EGG-LAYING MAMMALS, OR MONOTREMES. 



UNTIL recently it was an axiom in Zoology that 

 Mammals * were broadly distinguished from Birds and 

 Reptiles by the circumstance that their young were 

 born into the world in a living condition ; whereas in 

 the two latter groups the young were developed from 

 eggs laid by the parent, although in a few Reptiles the 

 eggs were hatched within the body of the parent itself. 

 Within the last few years, however, it has been found 

 that two most remarkable Mammals confined to the 

 Australasian region differ from all other members of 

 the same great class, and resemble Birds and Reptiles 

 in that they actually lay true eggs from which the 

 living young are in due course hatched. This remark- 

 able discovery has shown that the living animals in 

 question are more widely separated from all other 

 existing Mammals than had previously been considered 

 the case; and since we have in late years become 

 acquainted with an extinct group of fossil reptiles 

 which shows some remarkable signs of affinities with 

 these egg-laying, or oviparous Mammals, our ideas of 



* Popularly known as quadrupeds, see page 13. 



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