Dentition of Mammals. 283 
EDENTATES: embryos of Dasypus novemcinctus exhibit the 
typical formation of successors for the first seven teeth; a 
successor 1s wanting only in the case of the last tooth. The 
occurrence of tooth- “change in this animal has already been 
demonstrated by Tomes. Moreover in the lower jaw of the 
embryos I find not eight teeth, but eleven, of which the three 
first are smaller and do not cut the eum. I am now also 
able to mention a second Edentate which has rudiments of 
two dentitions: this is Dasypus villosus. This phenomenon 
consequently appears to be of very general occurrence among 
the armadilloes. Whether actual tooth- change really takes 
place is of no consequence for my purpose ; i merely affirm 
the presence of rudiments of milk and second teeth. 
MarsuPIALs: Flower, who was afterwards followed by 
Thomas, bases his hypothesis that the milk-dentition is a 
secondary acquisition on the part of the higher mammals, on 
What takes place in Marsupials, in which either no tooth- 
change or only the change of a third premolar occurs. The 
dentition of Marsupials is very generally assigned to the 
second series, and the precursor of the third premolar regarded 
as a milk-tooth, My own investigations upon this group 
have so far extended only to the study of a series of young 
specimens of Didelphys of different sizes. On the basis of 
these investigations I assert that THE PERMANENT SET OF 
TEETH 1S TO BE ASSIGNED TO THE MILK, OR FIRST DENTITION, 
and that only one second tooth, the subsequent third pre- 
molar, occurs. I can easily furnish the proof of this, as soon as 
it is eranted, that the two dentitions are also distinguishable 
from the point of view of morphology, besides being so from 
the physiological standpoint of the difference in the time of 
their appearance. ‘The rudiments of the two dentitions, 
which have a common origin in the primitive dental fold, are 
so disposed, that the first set of teeth is developed from the 
outer one, and the second from the inner. Now my prepa- 
rations show that this is the case not only in the third 
premolar, but that the tooth-rudiments lying in front of it, 
especially those of the incisors, also possess on the inner side, 
branching off from the neck of the epithelial invagination, a 
distinet twig of epithelium with a knobbed end; and this 
must be regarded as the earliest rudiment of the enamel- -organ 
of the second tooth. It at all events follows from this that 
the entire dentition of the opossums is to be ascribed to the 
first and not to the second series. ‘The mainstay of the hypo- 
thesis of Flower and ‘Thomas, that the milk-deritition has 
been secondarily acquired by the higher mammals, is thus 
destroyed, 
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