572 Mil. M. r. wooDWAED ON [May 5, 



series, whereas in Centetes this tooth is developed nearly as soon 

 as the undoubted milk-teetli and is shed about the same time as 

 the members of that series. 



On investigating the development of [^ no indication vchatever 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, a;), 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 eai-lier dentition. One might therefore be justified 

 in regarding this structure in Centetes as the last trace of d'- 3 , 

 and the functional tooth though early lost as p'-3 . I am, howevfir, 

 very doubtful as to the advisability of basing a conclusion upon 

 such slight evidence, more es])ecially as I have never observed an 

 undoubted reduced labial tooth in such a position, Aestiges of an 

 earlier dentition being always, so far as I am aware, related directly 

 to the dental lamina, i. e. 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 Ertnaceus, I 

 venture to suggest that this single i^ of Centetes belongs to the 

 permanent dentition, but that it is vei'y early developed and shod 

 with the milk-teeth. 



It is interesting to note that in the closely allied genus Ilcmi- 

 centetes a 3rd upper incisor is present in the adult dentition ; but 

 although we know a little of the tooth change in this form (3. p. 75), 

 yet we do not for certain know if this tootli is preceded by a 

 functional milk-incisor. 



i 1 i 2 



The remaining incisors T^-j-V4,--q together with the caninea 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 much 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 (polyprotodont 

 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 



