DEVELOPMENT AND SUCCESSION OF TEBTH IN PERAMELES. 561 
though, of course, no longer upon the grounds of the ab- 
sence of what he regards as rudiments of possible successors. 
But the latter he would prefer to relegate to the category of 
Leche’s fourth (post-sucvessional) dentition. His reasons for 
such a decision are largely of a speculative character. 
But there is one feature of his case which is by no means 
merely theoretical, but is based directly upon observation of 
structure. We refer to the presence of alleged rudiments of 
a molar dentition older than the existing molar series. We 
shall recur to this subject presently. 
We have examined several series of sections of early Ma- 
cropus embryos, and, like Woodward, we there find that the 
large and deeply cupped molar enamel-organs are as yet indis- 
tinguishable from the dental lamina, the latter appearing for 
the time being to have been wholly converted into the cup-like 
enamel-organs. But this is precisely what we find to be the 
case with the milk enamel-organs of the incisor and canine 
teeth in embryo pigs of 20 mm. head-length, where of course 
successional teeth arise later on. It is entirely a question 
of the stage of advancement of the developmental processes. 
And however it may be in Macropodidx, there is not the 
slightest doubt that lingually placed “ residual” prolongations 
of the dental lamina (and with swollen free distal margin) do 
occur constantly in Pe rameles during the development of every 
one of the molars, as shown in our descriptions and figures. 
Thus fig, 27 shows the tolerably early appearance (Stage 111) 
of the residual lamina by the side of m4. Here there can be 
no possible confusion with the Anlage of m2 which is seen in 
the horizontal sections (figs. 25 and 26) to be just developing 
further back. That the evidence derived from these horizontal 
sections is not to be gainsaid becomes apparent in the exami- 
nation of Stage 1v. There m2 is a well-developed cupped 
enamel-organ, and has itself developed a definite residual 
lamina with a swollen fundus (fig. 52), while beside m+ 
the residual dental lamina is seen persisting as a typical 
“ Ersatzleiste,” and appears on cross-section as a swollen 
and “ bud-like” (“‘knospenférmig ”) downgrowth (fig. 51). 
