570 J. T. WILSON AND J. P. HILL. 
The remaining figures (text-fig. 3, a, B, and c, and figs. 
84 and 85) from the pig are taken, not from the molar 
region, but from much more anterior parts of the jaws, in 
order to show the striking appearances in the way of labial 
processes which are produced at certain stages of the differ- 
entiation of the common Anlage of labio-alveolar groove and 
proper dental lamina. Attention may be especially directed 
to the transitional forms of the labial projections in the upper 
and lower jaws figured in figs. 84 and 85. It must be men- 
tioned that every one of the labial projections figured has 
actually been traced into continuity with the definite lip- 
furrow Anlage as clearly as in the case of the series shown in 
the first four outline figures (text-fig. 2) taken from the molar 
region. With regard to the latter it may be remarked that, 
as might be expected from the fact that the more immature 
portion of the molar lamina is the posterior, the primitive 
connection of the Anlagen of labio-alveolar and proper dental 
lamina is recognisable behind, and in proceeding forwards in 
the molar region a transition toa state of mutual independence 
of the two structures occurs. The fact that again, anteriorly, 
there is areturn to the status of a common Anlage is doubtless 
conditioned by other developmental factors. 
Comparison of fig. 83 and text-fig. 2 of the molar lamina in 
the pig, with figs. 30 and 31 of Stage 111, and 52—54 of 
Stage 1v of Perameles, and also with Woodward’s figs. 25a 
and 25 6 of Petrogale, will hardly fail to carry conviction of 
the essential identity of the structures therein represented. 
From a careful investigatiou of these labial appendages in 
the molar region we therefore conclude that while such ap- 
pendages may not be uniformly homologous, yet those which 
alone are definite, and irreducible to the results of unimportant 
incidents of development, require a different mode of inter- 
pretation from that suggested by Woodward. We must accord- 
ingly dismiss the idea that any structural features occur in the 
development of the marsupial molars which can fairly be 
interpreted as vestiges of degenerate “‘ milk” predecessors. 
We are thus thrown back upon the already noted resem- 
