54 TEETH OF CAPE ANTEATER CHAP. 
same phenomenon; for Sir W. Flower showed, and Mr. Thomas 
confirmed his discovery, that only one tooth, according to Mr. 
Thomas the fourth premolar, is replaced in that group. But 
even the purely monophyodont dentition of the Toothed Whales 
is a more apparent than real contrast to the diphyodont dentition 
elsewhere prevalent. An investigation of the embryos of various 
Toothed Whales by Dr. Kiikenthal and by Dr. Leche has brought 
to light the highly important fact that two dentitions are present, 
but that one only comes to maturity; from this fact obviously 
follows the interesting question :—To which of the two dentitions 
of more normal Mamunalia does the monophyodont dentition of the 
Whales and Marsupials belong? To this question a clear answer 
is fortunately possible. As has been pointed out in the fore- 
going sketch of tooth development, and has been illustrated in 
the figures, the milk teeth develop as lateral outgrowths of the 
common enamel germ, while the permanent teeth arise from the 
end of the same band of tissue. This fact enables it to be 
stated apparently beyond a doubt that in the Whales and in the 
Marsupials it is the milk dentition which is the only one to 
arrive at maturity. Thus the earlier theoretical conclusion that 
the Marsupial dentition “is a secondary dentition with only one 
tooth of the primary set left,” is proved on embryological grounds 
to be untrue. But there are other monophyodont animals than 
those already mentioned.' Orycteropus, the Cape Anteater, is an 
example. Mr. Thomas has lately discovered that in this Eden- 
tate there is a set of minute though calcified milk teeth which 
probably never cut the gum; here we have a different sort of 
monophyodontism, in which the teeth belong to the second and 
not to the first set. Between the latter condition and the 
diphyodont state are intermediate stages. Thus in the Sea Lions 
the milk teeth are developed but disappear early, probably before 
the animal is born. 
In the typical diphyodont dentition, such as is exhibited for 
example in Man and the vast majority of mammals, the milk teeth 
eventually completely disappear and are entirely replaced by the 
permanent set of teeth, with the exception, of course, of the molars, 
which though they are developed late belong to the milk series. 
' It would be of the greatest interest in relation to this and many other 
problems to ascertain the precise meaning of the monophyodont dentition of 
Ornithorhynehus. 
