546 J. T. WILSON AND J. P. HILL. 
markedly distinct in other respects from the original view of 
Thomas and Flower, for it is framed in full view of the pre- 
sence of those ingrowths of the dental lamina which, in 
common with Kikenthal, Rose, and others, he regards as rudi- 
mentary enamel-germs. These, however, he interprets not as 
the retrogressing vestiges of an older, but as the products of a 
progressive evolution heralding the advent of an entire new 
dentition, which among the Eutheria has arrived at a con- 
dition of greater or less completeness. We have seen, too, that 
Leche’s theory is widely different from that of Flower and 
Thomas in that he holds fast the homology of the marsupial 
teeth to the milk dentition of Eutheria; in his opinion it is 
the “second” dentition, not the “ first,” which is in process 
of acquisition. 
In supporting his theory Leche refers to the difficulty which, 
as we have already seen, was experienced by Thomas in re- 
conciling the condition observed in Triconodon with Kiken- 
thal’s theory of the vestigial character of the second dentition 
in modern Marsupials, and he claims that the difficulty vanishes 
when his theory is adopted, since he is able to point to the 
peculiar adaptation of the marsupial mouth to the sucking 
function as a cause adequate to account for the prolonged failure 
to develop a second dentition in the anterior region of the jaw. 
Leche would thus figure as a supporter of the original 
monophyodontism of Marsupials, were it not for the considera- 
tions introduced by his highly significant discovery of calcified 
vestigial teeth. These he interprets as belonging to a “ pre- 
lacteal ” dentition, since they are evidently antecedent in de- 
velopment to the existing adult teeth in these animals. 
Leche’s Denial of the Vestigial Character of the 
Supposed Second Dentition of Marsupials. 
If the theory of the persisting teeth of Marsupials, which is 
held by Leche in common with every recent investigator, be 
conceded, it is not easy to follow Leche in his opposition to 
the Kiikenthal-Roése doctrine of the vestigial character of 
the supposed successional enamel-germs. It is true he simply 
