558 MB. M. r. WOODWABD ON [Mft}' 5, 



one for those teeth, then we find this type apparently preserved in • 

 all its purity in certain living Insectivores (Oentetes, Ericulus, and 

 others), a condition almost unique amongst living mammals ; in 

 addition, some Insectivores exhibit molar teeth which ai'e supposed 

 to be but slightly in advance oH this, having acquired a small heel 

 above and below, thus presenting to us the trituberculo-sectorial 

 type (well seen in the upper molars of Tapaia, Sorex, &c., and in 

 the lower molars of the C'enletidix and Chrysochloris). 



On the other hand, in many respects the dentition of this order 

 cannot be regarded as primitive, for the ante-molar teeth are 

 obviously specialized both with regard to their form and number. 

 The molars, too, in many genera are clearly modified from a 

 tritubercular standpoint, the upper molars being often quiiique- 

 tubercular, while below the heel may attain equal importance with 

 the trigon and develop numerous cusps; in others the paraconidis 

 lost, thus producing a quadritubercular crown, an admittedly 

 specialized type of lower molar. 



As a whole the teeth of this order are characterized by the 

 strong development of their cusps, a condition closely associated 

 with their insectivorous diet ; this, jierhaps, accounts for their 

 resemblance to the teeth of the early Jurassic mammals, it being 

 highly probable that the latter were also insectivorous. If this 

 was the case, then the presence of these supposed primitive tooth- 

 patterns among living Insectivores may be due rather to tlie similar 

 nature of the food of these two groups, so widely separated in time, 

 than to an actual persistence of the unmodided tritubercular 

 molar from Mesozoic times until to-day. 



Until recently it was generally supposed that the Insectivora 

 were quite normal in their tooth change, Owen (18), Eousseau 

 (21), Dobson (3), and others describing a full milk-dentition 

 in some genera. But at the same time, it was known, from the 

 researches of fcipenco Bate (1) on the Mole {Tulim), that the milk- 

 dentition might be very tvansitoiy. 



Eecently Leche (7 & 9) has published the results of an inves- 

 tigation concerning the relationships of the milk and permanent 

 sets of teeth in a number of genera, adopting the more modern 

 methods of niicrotom}' to aid him in his researches, which were 

 extended to fastal as well as numerous stages after birth, until the 

 full adult dentition was acquired. 



In his first and preliminary communication, Leclie (7) came to 

 the most interesting conclusion that in the anterior tooth-region 

 of the adult Erinaceus a mixture of milk and successional teeth 

 was to be met with. The adoption of these results unfortunately 

 led me to put forward the view (30) that Ei-inaceus, in respect to 

 the relation of its sets of teeth, was intermediate between the 

 marsupial condition with its persistent milk set and the typical 

 diphyodont placental stage. This now turns out to be quite 

 erroneous, for Leche, in his later and complete work (9), shows 

 conclusively that Erinaceus possesses vestiges of two complete 

 dentitions, Jind that those anterior teeth, «'hich are apparently only 



