TOOTH-GENESIS IN THE CAVIIDE. 279 
mentions having examined one stage of this species with a head- 
length of 1°5 cm., and he mentions that neither 7. 2 or m.3 were 
developed. Now in Cavia we have seen that the anterior cheek- 
tooth present does not develope until after the appearance of 
the second and third. Similarly, in the dog I have shown (loc. 
cit.) that the smal] anterior premolars do not appear until some 
time after the larger posterior ones. According to Flower and 
Lydekker [5, p. 450] the first upper premolar is “small and 
deciduous.” It therefore seems possible, if not probable, that 
the tooth which Adloff identifies as Pd. 2 is in reality Pd. 3, that 
is the posterior deciduous tooth. Now the deciduous tooth in 
the guinea-pig I have shown to be developed in series with the 
molars, and in them I have shown the presence of “ concentric 
bodies” which I regard as milk vestiges. In like manner, there- 
fore, the so-called Pre-milk representative in connection with this 
tooth might be so interpreted. Whether this be the correct 
explanation or not, I do not consider it possible to identify the 
teeth from the examination of the condition found in a single 
specimen. 
With regard to Pd.3 in Cavia, I think the interpretation 
given by Adloff is erroneous, since he appears to have missed the 
peculiarity of the tooth-change; the “‘prilakteale Anlage” in 
this case being identical with the “ concentric body.” 
As to the incisors in Spermophilus I am unable to express 
a definite opinion, not having had an opportunity of examining 
a specimen; nevertheless I would point out that Iam not in 
accord with Adloff in his identification of dentitions, and the 
interpretation previously given with regard to the incisors in 
‘Cavia probably applies equally in the case of Spermophilus. 
I claim to have shown reason for believing that the existence 
of pre-milk vestiges in the Rodents is still ‘““non proven” ; and I 
cannot refrain from quoting Woodward, who, though a believer 
in their existence, and having carried out extensive researches 
on the dentition of the Rodents, says [27]:—“ I do not think it 
is probable that we should find traces of such a vestigial structure 
persisting in a specialized group like the Rodentia; the ancestry 
of which are to be sought according to Cope in the generalized 
Tillodontia, who in all probability possessed a typical milk- 
dentition which has become gradually suppressed as their 
descendants became more and more specialized.” 
20* 
