472 J. 2. WILSON’ AND? 7, °P. Bibi: 
As in Perameles, but in much more marked degree, the 
third is the largest and most advanced in its development 
among the upper incisors. Here (fig. 23) the definitive cup- 
ping of the enamel-organ of 2%, has at last been effected, and 
a well-marked dermal papilla (mp. i*) formed, while at the 
same time the main body of the dental lamina has undergone 
such differentiation that the mass of cells forming the lingual 
portion of the cupped enamel-organ is now becoming distinct 
from the rest of the dental lamina. The latter is, in fact, in 
process of liberation as a “residual”? dental lamina (rdi.). 
(In an antecedent stage the Anlage of 73 is found to be differ- 
entiated to exactly the same extent as the corresponding 
Anlage in Stage 111 of Perameles.) A remarkable feature 
in this section is the rudimentary di3. Whatever may be 
said in detraction of the claims of the structure we have 
described in connection with 72 in Perameles, to figure as a 
vestigial enamel-organ, it is impossible to deny that here in 
Dasyurus we have an indubitable vestigial predecessor to 
28, It seems to us impossible to gainsay the homology 
testified to by this comparison between Perameles and 
Dasyurus. And it is superfluous to point out that an ad- 
mission as regards the identity of the structure labelled di2 
in Perameles with the vestigial tooth in Dasyurus involves 
the admission of a similar homology for the structures in 
Perameles in series with “di3.” Here in Dasyurus 
(fig. 23) di= is not simply a degenerate cell-mass, but has 
assumed specific dental characters by the precocious evolution 
of a small but thick dentine cap, which again is covered bya 
hood of regularly arranged enamel-cells. Instead of forming 
a projection from the rest of the incisor mass, the vestigial 
tooth rather lies embedded in the labial aspect of the latter 
near its base. Perhaps this may be explained by a reference 
to the great labial outgrowth of the Anlage of the permanent 
incisor which must have occurred to bring about the condition 
figured, together with the later stationary and unprogressive 
character of the calcified vestigial di%. 
The examination of an earlier stage of Dasyurus has 
