ECHIDNA WALKING. 
CHAPTER XXXVII. 
Egg-Laying Mammals, or Monotremes,— Order Monotremata. 
The Australasian mammals, known as the duckbill and the echidnas, differ from 
the other members of the class not only in certain important structural points, but 
also by their young being hatched from eggs laid by the female parent. In their 
structural differences, and in their mode of reproduction, they resemble reptiles, 
although they agree with other mammals in that the young, when hatched, are 
suckled by milk secreted by the mother. Owing to these great differences, the 
Egg-laying Mammals, or Monotremes, as they are technically termed, constitute not 
only a distinct order (. Monotremata ) in the class, but form a separate subclass 
known as Prototherians ( Prototheria ). Consequently we find that Mammals are 
divided into three primary groups or subclasses, viz.: 
1. Eutherians, or Placentals, containing the first nine orders. 
2. Metatherians, or Implacentals, including the Pouched Mammals. 
3. Prototherians, represented only by the Egg-laying Mammals. 
These Egg-laying Mammals have no immediate relationship to Birds, but are 
closely allied to certain extinct orders of Reptiles and Amphibians; and the 
present representatives of the group are highly specialised creatures, and thus 
widely different from the original ancestral types of the Mammalian class, 
which we may fairly presume to have once existed as members of the Prototheria. 
Such ancestral types were doubtless furnished with a full series of teeth of a 
