Mr. W. H. Flower on the Teeth in the Marsupialia. 133 



appears almost paradoxical to suggest that the milk- or deciduous 

 teeth may rather be a set superadded to supply the temporary needs 

 of mammals of more complex dental organization. But it should be 

 remembered that, instead of there being any such relation between 

 the permanent and the milk-teeth as that expressed by the terms 

 "progeny" and "parent" (sometimes applied to them), they are 

 both (if all recent researches into their earlier development can be 

 trusted) formed side b_y side from independent portions of the pri- 

 mitive 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 fuuctionless or, as it were, partially 

 developed state. The milk-premoiars of some Rodents (as the 

 Guinea-pig), shed while the animal is in ntero, 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 deca- 

 dence, or, perhaps, absence of some of the second or so-called per- 

 manent 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 modi- 

 fied members of groups in the other members of which the same 

 phenomenon does not occiir, as in Cheirowys among the Lemurs, 

 Trichechus 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 sac- 

 cular stages of milk-predecessors to other of the teeth besides those 

 determinate four in which, for some reason at present unexplained, 

 they arrive at a more mature growth*. Such proof as this would 

 alone decide the truth of these speculations ; and I have not at pre- 

 sent either the requisite leisure or materials for following out so 

 delicate an investigation. I trust that the facts already elicited are 

 suflficiently novel and important to justify my bringing them, as they 

 now stand, before the Society. 



* It may be remarked that the milk-tooth which alone is developed in the 

 MarsuiDials corresponds honiologically 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. 



