ro2 TEETH OF EDENTATES CHAP. 
inasmuch as many Kdentates have teeth. It is, however, by 
a number of small tooth-characters that the order can be 
defined. Thus if teeth are present they are simple in struc- 
ture, without enamel in the adult condition, though a rudi- 
mentary enamel-organ has been discovered in an Armadillo. 
.The teeth, moreover, are not found in the anterior part of the 
mouth, and they grow from persistent pulps; neither is there 
much differentiation among them. It is not possible, however, 
to speak of the Edentates as quite homodont, since in Oryeteropus 
there are large cheek-teeth ; but there is at any rate not a marked 
heterodonty in that or in any other Edentate. It used to be said 
that the Edentates were monophyodont. But the Armadillo 
Tatusia was subsequently found to possess a second suppressed 
dentition, and after this discovery Mr. Thomas proved that 
Orycteropus is also diphyodont. Since then other Armadiilos 
have been shown to be diphyodont; and the whole group there- 
fore, so far as concerns those members that have teeth, may in ail 
probability be regarded as typically mammalian in this respect. 
These characters are slender enough, but there seem to be 
no others by means of which the members of this order can be 
satisfactorily linked together. The fact is, that we have here 
a polymorphic order which contains in all probability repre- 
sentatives of at least two separate orders. We have at present 
a very few, and these perhaps highly modified, descendants of a 
large and diverse group of mammals. For convenience’ sake they 
will be all treated of under the head of Edentata. 
Although for the probable reasons already stated it is a 
hard matter to frame such a definition as will inelude all 
existing Edentates, it is easy enough to define two groups in this 
heterogeneous order; to define one group we should say, rather, 
and then to regard the leavings as forming another not so easily 
definable a group. 
The perfectly-definable group is that which includes the 
American Anteaters, the Armadillos, and the Sloths. In all 
these creatures, which may certainly be regarded as representing 
on their own account as many family types, there are a number 
of important and highly-characteristic anatomical features which 
they share in common. So exceedingly different are these three 
types in general appearance and (correlated with that) in way of 
life that these common characters acquire increased importance. 
