DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 467 
growth is further seen to be the seat of retrogressive processes, 
for in neighbouring sections it shows invasion by connective 
tissue, partially breaking it up into smaller cell-groups. 
This cell-mass is incontrovertibly the serial homologue to 
the projection figured under “ di2” in the region of the second 
incisor in figs. 17 and 18, though plainly it is in a more ad- 
vanced phase of evolution, as its greater isolation from the 
main mass and condition of degeneracy testify. We are 
satisfied that this cell-mass can be regarded as none other 
than the degenerating remains of that very early, labially 
placed enamel-organ, which we have described and figured 
above (p. 454, and figs. 2, 3, and 4) in connection with a pro- 
minent swelling of the incisor region of the dental lamina in 
the preceding Stage u. It will be remembered that the 
localised thickening of the dental Jamina was set down as the 
Anlage of 78, and the labially developing enamel-organ, im- 
perfectly approximating to the cupped stage, was regarded as 
that of di3. The judgment there expressed on the strength 
of our observations upon the differentiation of the dental 
lamina in that stage, is now seen to be borne out by the degree 
of development subsequently attained by the presumably ho- 
mologous structures. 
It is interesting to note that in the present stage, as in the 
preceding, the third incisor Anlage as a whole is still the most 
bulky of the incisor series, although the disproportion between 
it and the other incisor Anlagen is now greatly diminished. 
It must be noted in regard to fig. 18 that, in a longitudinal 
section passing so near to the base of the dental lamina in the 
73 region as that figured, it is only the basal portion of the 
Anlage of 73, and the vestigial remains of d2, which are 
recognisable. Itis only at higher planes that the differentiation 
of the Anlage of i2 into labial and lingual lobes is as recog- 
nisable as it is, e.g. in the case of 72 in the same section. 
Lower down in the case of the latter region, indeed, the labial 
portion of the Anlage of 72 similarly disappears from the 
section as a distinct lobe, leaving only the common lamina 
plus the labial projection of di2. 
VoL. 89, PART 4, 
NEW S5ER. K K 
