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could wish, but I think on phylogenetic ground based partially on 
palaeontological evidence and on the general consideration of the sup- 
posed evolution of the sucking Mammals with their reduced dentition 
from the egg laying reptile with its polyphyodont dentition [see Kixen- 
THAL (15), Leche (2—5), Woopwarp (16), Röse (1)| we are forced to 
the conclusion that a small set of teeth must have existed and has 
since been lost (or almost so) during that evolution, and of this set 
the last traces are seen in the premilk dentition. 
In the evolution of the enlarged heterodont dentition of the Mam- 
mal from its polyphyodont reptilian ancestor, we must beleive either 
that one set of teeth became enlarged or that there was a fusion of 
two or more adjacent sets, both of which views necessitate a reduction 
in the number of sets of teeth, a condition which we find in the juras- 
sic Mammals and also in the living Marsupials. 
The next important question is which set or sets of teeth would un- 
dergo this change? Would the first set be included in this specialization ? 
This last question I think we may safely answer in the negative, for this 
early ancestor of the Mammalia was probably still in the reptile stage, 
inasmuch as it was hatched out of an egg and its parents had not yet 
developed mammary glands, it was therefore necessary for this young 
animal to feed itself, a process necessitating the presence of teeth as 
soon as it was born, now this beast had only a very small jaw incapable 
till grown bigger of lodging the enlarged heterodont dentition which 
would like most recently developed characters appear late, therefore I 
think we must assume and with fair reason, that a small temporary 
set of teeth would be retained for the use of the young animal, while 
the enlarged heterodont dentition was developing deeper in the jaw, 
this latter coming into use as the jaw enlarged with age. This tem- 
porary set which would be developed in the anterior part of the jaw 
only is the premilk dentition, once of great importance to the animal, 
but now, since the appearance of mammary glands which provide the 
young with nourishment during its early life, has lost its function and 
is only retained as functionless tooth vestigies in the lower Mammals. 
The earlier development of the milk set (the first acquired heter- 
odont dentition) was also due to this better supply of nourishment and 
perhaps to the fact that the character (the enlarged set of teeth) had 
become a permanent feature of this animal and consequently like most 
morphological characters tended to develop earlier. This may have 
given the germs of the successional teeth a chance to reappear, they 
never have been entirely suppressed but only indefinitely retarded. 
An analogous condition is seen in the Insectivora (4, 14) where 
