DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES, 401 
Part II.—Description oF Stages, 
Stage I.—Perameles obesula: intra-uterine embryo. 
Length from anterior convexity of head to curved hinder 
extremity of body ' : ; . 875 mm. 
Coronal and sagittal series examined. 
This stage is that in which an allantoic placenta has been 
described by one of us (H., 30). 
The margins of the gap are not yet soldered together to 
form the “ Saugmund.” 
As regards its tooth development, this stage appears to 
correspond pretty closely to that described and figured by 
Rose as his earliest stage in Didelphys (1, p. 641, fig. 1). 
The structure referred to by Rose as “ einer leicht ins Kie- 
fermesoderm eingesunkenen Epithelwucherung,”’ and labelled 
“7.1.” in his fig. 1, is present in our specimens in both upper 
and lower jaws. In the upper jaw a very shallow groove like 
that shown in Rose’s figure appears abruptly a little behind 
the anterior end of the jaw. ‘This faintly indents the surface 
of a slight thickened ingrowth of the oral epithelium into the 
mesoderm. Both groove and solid cellular ingrowth when 
traced backwards gradually fade away, the superficial groove 
disappearing sooner than thesolid proliferating band of epithelial 
cells. 
In coronal sections of the lower jaw a lens-shaped thicken- 
ing of the oral epithelium is first met with anteriorly. Soon 
a shallow groove appears over this, and the thickening then 
dips more deeply into the mesoderm, becoming almost tri- 
angular in cross-section. Further behind, the groove becomes 
description of a slide is thus easily condensed into a series of notes, each pre- 
faced by a formula expressive of the individual section to which the note 
refers. Frequently one wishes to refer to a number or groups of sections at 
one time. ‘This is obviously to be accomplished by extending the upper line 
18-26 
6—-lI-E 
sixth row of the third slide of series E is conveniently indicated. This 
method is specially useful for reference from drawings to the sections 
figured. 
VOL. 39, PART 4.—NEW SER. 11 
of the formula thus :— Here a group of eight sections in the 
