DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES, 509 
itself. No one viewing our fig. 33 can doubt that 7, isin some 
sense successional to our vestigial diz, as there illustrated. 
It must be borne in mind that the first lower incisor of the 
adult is a large and forwardly growing tooth. We have already 
seen that its Anlage is at first placed behind that of its small 
and rudimentary milk predecessor, but that subsequently the 
latter appears as if displaced backwards, owing to the anterior 
extension of the large permanent tooth. In lke manner, we 
believe that this forward growth of 7; accounts for the note- 
worthy change in the later topographical relations of 2; to the 
rudimentary enamel-germ produced from a segment of the 
dental lamina, which in earlier stages is entirely in front of it. 
We think it most probable that the rudiment in question 
really represents an incisor which has been lost, in front of 
2,, and which appears in imperfect form, and for a short time 
only, during ontogeny, before the very great forward extension 
of 7; wholly prevents its further development. Its continuity 
posteriorly with the residual lamina of 7; according to our 
views proves nothing one way or another with re- 
gard to its successional character, for everywhere we 
find that it is the residual lamina in the region of a tooth 
which is the true morphological continuation of the undif- 
ferentiated dental lamina in front or behind it. 
It is interesting to compare the condition in Perameles 
with that described by Mr. Woodward for Petrogale (2). 
In that form he found two small calcified vestigial incisors. 
The anterior of these was entirely in front of the large per- 
manent lower incisor, which latter he therefore regarded as 
really an ?z. 
In connection with his vestigial first incisor (regarded by 
him as belonging to the first dentition) he describes and figures 
a lingual downgrowth of the dental lamina showing clearly 
the papillated enamel-germ of a successional tooth (see his 
fig. 10). Now we have shown (see our fig. 33) that our vestigial 
di, is related thus, not to a rudimentary successional tooth- 
germ, but to the adult 7;. It is evident, therefore, either 
that 7; of Perameles is not homologous to the adult per- 
