TOOTH-GENESIS IN THE CAVIID®. 275 
Having now given an account of the conditions found in these 
various stages, the question arises as to what interpretation may 
be placed upon them. In the first place, it will be noted that 
the deciduous tooth is the first to arise, or at least is the more 
advanced in the first stage examined. In tracing its subsequent 
development, it does not appear to be connected with any germ 
which could be interpreted as either a predecessor or a successor: - 
in other words, this tooth seems to be represented in one denti- 
tion only, and it might be either a milk-tooth the successor of 
which had become suppressed, or vice versa; and I know of no 
definite data upon which to form a decided opinion. The fact 
of its early appearance, and of its being shed zn utero, might 
seem to favour the former alternative. J am inclined, however, 
to regard it as a permanent tooth accelerated for the following 
reasons :—(1) its development is but little in advance of the 
incisor or of the molar immediately behind it, both of which are 
known to belong to the second dentition; (2) in the dog the 
carnassial tooth of both dentitions is developed in advance of the 
other teeth, which supports the view that teeth in this position 
have a tendency to become accelerated; and (3) I believe that 
the dentitions in the Mammalia tend to disappear from without 
inwards. 
This being so, I would regard all five tooth-germs found in 
the guinea-pig as belonging to the permanent series, the first and 
fourth having, in my opinion, vestigial remains of milk predeces- 
sors in the “ concentric bodies”’ afore described (Pl. 26. fig. 7). 
Though the pattern of the so-called molars and premolars in 
the adult Cavia are practically identical, still in their earlier 
stages they are somewhat different, the anterior cheek-tooth 
being transversely broader and more multitubercuiate than the 
posterior ones. The deciduous tooth appears to me to partake 
more of the nature of the latter; and I am inclined to believe 
that it is to be regarded as the anterior molar, thus agreeing 
with the suggestion first made by Woodward in relation to other 
mammals. 
The tooth which replaces the deciduous is the anterior cheek- 
tooth, which is not therefore its true morphological successor, 
but merely drops backwards and occupies its position. 
In this connection it is interesting to note what Forsyth 
Major says [8] in referring to Prolagus sardus :—“ The anterior 
of the three deciduous teeth is not situated directly above the 
