Bae J. T. WILSON AND J. P. HILL. 
novel and revolutionary view that the deciduous tooth of 
Perameles, and probably of other Marsupials, was a member 
of a supposed degenerate “prelacteal” series. But ere long 
we were led, first to call in question, and then confidently to 
reject the “ prelacteal” theory of this earliest tooth-series, as 
a violation of that principle of parsimony which should govern 
our procedure in the construction of explanatory hypotheses. 
For if dp. 3 and the supposed “ prelacteals”” be regarded as 
representatives of an otherwise suppressed milk series of mar- 
supial teeth, we shall have before us a workable hypothesis 
which we believe to be free from the difficulties and complica- 
tions which beset that more generally current, and which 
offers no insuperable difficulties of its own. 
In preceding pages we have dwelt upon the application of 
Leche’s criterion of the contemporaneousness of origin 
of the tooth-Anlagen from the dental lamina. We 
have shown that, judged by this test, dp. 3 belongs to a 
different category than that of the other persisting antemolar 
teeth. The identification of dp. 3 and the “ prelacteals” as 
members of one and the same tooth-series may be designated 
as a positive result of the application of the same cri- 
terion. The investigation of our Stages 11 and 111 has yielded 
the most striking evidence of the validity of such a conclu- 
sion. 
Thus in Stage 11 the enamel-organs of the future permanent 
antemolar teeth are in abeyance, or are represented only by 
localised undifferentiated thickenings of the dental lamina, 
But already dp? and di+ show well-marked cupping (figs. 8, 9, 
14, and 12), while d¢3 shows a slighter degree of it (figs. 2, 
8, and 4), and the enamel-organ of d£ is, at least, in process of 
differentiation from the main mass of the canine Anlage 
(fig. 13). 
But it is in connection with Stage 111 that the most strik- 
ing pictures are obtained. The horizontal series from this 
stage was of especial use to us during our period of transition. 
Specially would we refer to our fig. 22, as affording a most 
instructive comparison between the canine ‘ prelacteal ” 
