572 MR. M. F, WOODWARD ON [May 5, 
series, whereas in Centetes this tooth is developed nearly as soon 
as the undoubted milk-teeth and is shed about the same time as 
the members of that series. 
On investigating the development of i.3 no indication whatever of 
a reduced successor is to be met with, the dental lamina being com- 
pletely fused with the enamel-germ of this tooth, and consequently 
exhibits no lingual development. On the other hand, a slight out- 
growth from the enamel-organ itself is visible on the labial side 
(Plate XXV. fig. 25, x), very similar to that figured by Kiikenthal 
(6) in the Walrus (Taf. iii. fig. 7, rvz.), and which he there regards as 
the remains of an earlier dentition. One might therefore be justified 
in regarding this structure in Centetes as the last trace of di. 3, 
and the functional tooth though early lost as pi-8. I am, however, 
very doubtful as to the advisability of basing a conclusion upon 
such slight evidence, more especially as I have never observed an 
undoubted reduced labial tooth in such a position, vestiges of an 
earlier dentition being always, so far as I am aware, related directly 
to the dental lamina, 7.¢. to the neck of the enamel-organ of the 
replacing tooth and not to the modified body of that structure. 
Nevertheless, from the entire absence of any trace of a successor 
to this tooth and from the fact that the milk-dentition appears to 
be undergoing reduction in most Insectivores, and especially from 
the condition of the 3rd incisors in Gymnura and Erinaceus, I 
venture to suggest that this single i.3 of Centetes belongs to the 
permanent dentition, but that it is very early developed and shed 
with the milk-teeth. 
It is interesting to note that in the closely allied genus Hemz- 
centetes a 3rd upper incisor is present in the adult dentition; but 
although we know a little of the tooth change in this form (8. p. 75), 
yet we do not for certain know if this tooth is preceded by a 
functional milk-incisor. 
a Ne 
The remaining incisors 1,12 together with the canines and the 
three premolars above and below are all present as functional 
teeth in both dentitions. 
A very marked gap is noticeable between the canines and the 
first functional premolars both above and below: this tends to 
confirm the generally accepted view that the missing premolar is 
the 1st of that series. Unfortunately the dental lamina has been 
completely aborted from this gap in both stages examined, so that 
no indication of a missing tooth could be found. 
The diastemata between these teeth are uch more pronounced 
in the older stage and still more so in the adult; and from what 
I have seen in this and other long-nosed mammals (polyprotedont 
Marsupials), I am led to conclude that this elongation of the 
jaw is a secondary one, acquired since the reduction in the tooth 
series. This to my mind accounts for the absence of all vestiges 
of the suppressed teeth, for, when recently suppressed, tooth- 
vestiges are generally found even in short-nosed forms. The 
presence of four upper molars in this form appears to point to a 
