CEEAsP ARR. 
THE EXISTING ORDERS OF MAMMALS 
PROTOTHERIA—MONOTREMATA 
ApArT from those creatures whose fragmentary remains have 
been considered in the last chapter, and which belong to the 
earliest of mammaliferous strata, the remains of Mammalia are 
all referable to existing orders. In the pages which follow we 
shall therefore deal with the actual representatives of living 
families side by side with their extinct relatives. The existing 
orders of Mammalia, together with those of their fossil allies, can be 
plainly divided into two great subdivisions, or, as we shall term 
them, sub-classes; the Mammalia as a whole being termed a class 
of the Vertebrata comparable with the class Reptilia, ete. It 
has been usual, owing to the initiative of Professor Huxley, to 
divide the Mammalia into three divisions of primary importance. 
We shall adduce reasons later for not accepting this mode of 
division, but that which allows of only two primary divisions. 
These two divisions are (1) Prototheria and (2) Eutheria. 
Whether the Multituberculata, Trituberculata, and Tricono- 
donta, considered in the last chapter, are really to be distributed 
among these two sub-classes is a matter upon which it is possible 
to form an opinion, but not to dogmatise. The Prototheria 
stand at the base of the mammalian series, and present many 
likenesses to the Sauropsida; the Eutheria are the animals 
which are most fully differentiated as mammals. We shall 
commence eae 
SuB-Ciass I—PROTOTHERLTA. 
To this group belongs the order Monotremata, and possibly 
also the so-called Allotheria or Multituberculata. As, however, 
