DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 4738 
shown us the third milk incisor at a stage prior to its calcifica- 
tion as a deeply cupped enamel-organ structurally comparable 
to the enamel-organ of d‘, figured by us in Perameles 
(fig. 20). Thus we have shown that, in Dasyurus, the rudi- 
mentary enamel-organ of di2, does not undergo the rapid 
degeneration which is exhibited by di3, in Stage 11 of 
Perameles, but passes into the regular cup-shaped stage which 
we have seen in the upper jaw of Perameles to be attained 
only by d3. 
A thoughtful comparison of the following series of figures 
will render it easy to understand the derivation of the condi- 
tions found in the third incisor region of Dasyurus from the 
earlier condition illustrated in Stage 11 of Perameles: 
Cf. Perameles, Stage II, 73 and di in figs. 3 and 4, 
" epee LUN) Lares in figs. 17 and 18. 
9 oo sae eo in figs. 18 and 19. 
” ” » +(C and ds in fig. 20. 
In fig. 21 it is seen that the dental lamina is continued 
backwards, diminished but unbroken, from the region of the 
canine (marked “0. e.”) to a point where it somewhat suddenly 
expands to form the Anlage of the first premolar (p+). It 
will be evident from the figure that, though this enlargement 
appears as a general expansion of the lamina, the addition or 
increase of cell material is towards the labial side, so that the 
bulging is in that direction. On coronal section, indeed, one 
obtains an appearance not far removed from that exhibited in 
this same stage by 74, although it can hardly be said that a 
definite furrow has appeared between the labial bulging and 
the main body of the dental lamina. Both in figs. 21 and 22 
the stretch of dental lamina extending from the canine to the 
first premolar is recognisable. 
In the first-named figure, however, the section passes along 
the more constricted basal portion or ‘ neck” of the lamina. 
In the second figure the section passes through the lamina 
near its free margin or “ fundus,” where that reaches a high 
vertical extension in the neighbourhood of the canine. Further 
back the lamina disappears from the section by becoming ver- 
