510 J. T. WILSON AND J. P. HILL. 
manent lower incisor of Petrogale, or that our vestigial 
di is not homologous to the first vestigial incisor of Petro- 
gale. May it not be that an anterior milk incisor in Pera- 
meles has been entirely suppressed, and that its successful 
germ, serially homologous with 7;, attains a development in 
front of the first lower incisor, comparable to that of the suc- 
cessional germ connected with the first vestigial incisor of 
Petrogale? 
And may it not be that Woodward’s second vestigial incisor 
(his 7;), to which he was unable to recognise any successor, is 
really the homologue of our di; whose legitimate successor is 
Woodward’s iz, the almost certain homologue of our ‘‘7,” of 
the adult Perameles? 
An interesting modification in the relations of the vestigial 
first incisor (d?;) is seen in this stage. In the early stages it 
was seen to be attached intimately and directly to the neck of 
the main dental lamina opposite its connection with 2; (see 
fig. 83). In Stage v (fig. 66.) its attachment to the neck of 
the dental lamina is being, as it were, stretched away labially, 
thus tending towards the acquisition of an apparently inde- 
pendent attachment to the oral epithelium. This may be 
explained as effected, either figuratively or literally, by an 
opening out upon the deep surface of the oral epithelium of 
the most superficial part of the common lamina. In the 
present stage this process has been completed, and in fig. 66 
the vestigial di; is seen to possess an independent lamina of 
attachment to the deep surface of the oral epithelium labially 
from the line of attachment of the main lamina. 
It is such a process of opening out and labial dislocation as 
this, which we have already suggested as explaining the 
peculiar downgrowths on the labial side of the root of the 
dental lamina present in the first upper incisor region in 
Stages 1v and v (figs. 43—46 and p. 485). The present 
instance is an absolute proof of the possible occurrence of just 
such a dislocation of the primitive connection of a labial and 
more superficial member of the dental series. 
In this stage may be noted for the first time the differentia- 
