DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 547 
refuses his assent until further proof. But the reasons he 
urges in support of the alternative theory do not appear to us 
to be of a very convincing character. Those sceptical argu- 
ments which alone appear to us to be specially cogent as applied 
to the theory of Kiikenthal and Rése, and which we owe largely 
to the logic of Leche himself, appear to us to be almost equally 
destructive of the presuppositions of his own position. 
Leche first calls attention to the long persistence of the 
so-called “ enamel-germs of the second dentition.” We have 
already adversely criticised the idea, common both to Leche and 
his opponents, that genuine and actual successional enamel- 
germs are present. But even. supposing that such are really 
in evidence, we cannot see that their ‘‘ long persistence” is 
any argument against their vestigial character. On the con- 
trary, if they are really vestiges of teeth which have been lost, 
it is precisely these remnants of structures which formerly 
persisted throughout a considerable part of the life of the animal 
which will retain the strongest tendency towards durability. 
Again, the occasional occurrence in other mammals (e. g. 
Erinaceus and Phoca) as discovered by Leche of teeth of a 
third dentition, developed from outgrowths of a residual dental 
lamina by the lingual sides of teeth of the second dentition, 
does no doubt establish the capacity of the dental lamina— 
after partial exhaustion by the production of a first and a 
second dentition—to once more liberate itself as a free residual 
lamina, from which in rare cases there may actually be gene- 
rated members of a third and entirely new dentition. 
But just in so far as this argument is relied upon for Leche’s 
purpose his case is weakened for the establishment of the 
homology of the supposed potential enamel-germs of Mar- 
supials to the Eutherian second dentition, a case which is, at 
its best, in our opinion an exceedingly weak one. In fact, we 
may say that if the production in some mammals of teeth of a 
third dentition, from “enamel-germs” similar to those of 
Marsupials, be admitted, this may fairly be claimed as at least 
establishing, on Leche’s own premises, the possibility ofa 
true morphologicalcorrespondence between the similar structures 
VOL. 39, PART 4,.—NEW SER. PP 
