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ME. W. H. FLOWEE ON THE DEVELOPMENT AND 
them*, they are both (if all recent researches into their early development can be trusted) 
formed side by side from independent portions of the primitive dental groove, and may 
rather be compared to twin brothers, one of which, destined for early functional activity, 
proceeds rapidly in its development, while the other makes little progress until the time 
approaches when it is called upon to take the place of its more precocious locum tenens. 
Many facts appear to point to the milk-teeth as being the less constant and important 
of the two sets developed in diphyodont dentition. Among these the most striking is 
the frequent occurrence of this set in a rudimentary and functionless, or, as it were, 
partially developed state. The milk-premolars of some Rodents (as the Guinea-pig), shed 
while the animal is in utero , the simple structure and evanescent nature of the milk- 
teeth of the Bats, Insectivores, and Seals, the diminutive first incisors of the Dugongs 
and Elephants, all appear to be cases in point. 
On the other hand, examples of the commencing or sketching out, as it were, of the 
successors to a well-formed, regular, and functional first set of teeth are rarely, if ever, 
met with. Occasional instances of the habitual early decadence, or, perhaps, absence of 
some of the second or so-called permanent teeth occur in certain animals ; but these are 
rather examples of the disappearance or suppression of organs of which there is no need 
in the economy, and chiefly occur in isolated and highly modified members of groups in 
the other members of which the same phenomenon does not take place, as the Cheiromys 
among the Lemurs, Trichecus among the Seals, and the recent Elephants (as regards the 
premolars) among the Proboscideans. They form no parallel to the cases mentioned 
above of the rudimentary formation of an entire series of teeth of the temporary or 
milk-set. 
To return to the Marsupials : — If this view be correct, I should be quite prepared to 
find, in phases of development earlier than those yet examined, some traces either of 
the papillary, follicular, or saccular stages of milk-predecessors to other of the teeth 
besides those determinate four in which, for some unexplained reason, they arrive at a 
more mature growth f. Such proof as this would alone decide the truth of these specu- 
lations ; and I have not at present either the requisite leisure or materials for following 
out so delicate an investigation. I trust that the facts already elicited are sufficiently 
novel and important to justify my bringing them, as they now stand, before the Society. 
* Cyclop. Anat. and Phys. Art. “ Teeth,” vol. iv. p. 901. 
t It may be remarked that the milk-tooth which alone is developed in the Marsupials corresponds homolo- 
gically with that which, as a general rule, is most persistent in the typical diphyodonts, including Man, viz. the 
posterior milk-molar, replaced by the posterior permanent premolar. 
