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cisors, canines and posterior premolars as belonging to one set while 
the permanent canine and the first premolar belonged to a 24, the 
remaining permanent teeth being referred to a drd series, a conclusion 
which is contradicted by the study of other forms, as a matter of fact 
the time of first appearance of an enamel organ depends largely on 
whether a tooth is accelerated, retarded or reduced in its development. 
Further this tooth dpm 4 when not reduced does not differentiate at 
the same time as the anterior premilk teeth (Macropus). 
Neither does the similarity in position between these teeth stand 
for much for it is only in Dasyurus where dpm a is so vestigial 
that it occupies this extreme labial position, in the Macropodidae 
it develops in a line with and between the 3r4 premolar and the 1st 
molar and probably belongs to the same series as the latter tooth, 
being a true molar acceleratead and displaced (12 and 14). 
The resemblance between dpm 4 and the anterior vestigial premilk 
teeth is then probably only an apparent one due to the fact that both 
are disappearing and we shall not therefore be justified in regarding the 
anterior vestigial teeth as belonging to the milk set because of their 
resemblance to the vanishing dpm 4. 
In the anterior region of the jaw of the Marsupials we find then 
the following sets of teeth, (1) a small vestigial but often calcified set, 
(2) a large functional set and (3) a series of lingually placed swellings 
of the dental lamina (KUKENTHAL, Röse, LecHE and Woopwarp) 
closely resembling in appearance the first indication of the successional 
set in the Placentalia. It is now generally beleived that the 224 set re- 
presents the milk dentition and the 3rd the reappearing permanent teeth 
of the higher Mammals, the 1st set being regarded as a premilk den- 
tition. If the structures described by Röse and LrecHr in Man, the 
Ox and the Hedgehog are the homologes of the calcified labial 
teeth of the Marsupials, then there can be no doubt that this latter 
is a true premilk dentition, but these structures in the Placentalia 
are slight, though said to be constant and some may doubt the cor- 
rectness of this interpretation especially on comparing these labial teeth 
with the undoubted reduced milk dentition in many insectivores, and 
they may consequently be inclined to regards as Tims (17) has the 
labial toothlets of the Marsupials as reduced milk teeth, and thus re- 
turn to the discarded FLowER and THomas (18) hypothesis. It will 
not doubt be difficult to convince such beleivers that their interpret- 
ation is incorrect until we can find some premilk teeth in the Pla- 
centalia better developed than those of LecHe and Röse and we can 
only admit that ontogeny is not as conclusive on the point as one 
