558 MR. M, F. WOODWARD ON [May 5, 
one for those teeth, then we find this type apparently preserved in 
all its purity in certain living Insectivores (Centetes, Hriculus, and 
others), a condition almost unique amongst living mammals; in 
addition, some Insectivores exhibit molar teeth which are supposed 
to be but slightly in advance of this, having acquired a small heel 
above and below, thus presenting to us the trituberculo-sectorial 
type (well seen in the upper molars of T’upaia, Sorex, &c., and in 
the lower molars of the Centetide 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 quinque- 
tubercular, while below the heel may attain equal importance with 
the trigon and develop numerous cusps; in others the paraconid is 
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, perhaps, 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 the similar 
nature of the food of these two groups, so widely separated in time, 
than to an actual persistence of the unmoditied 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), Rousseau 
(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 Spence Bate (1) on the Mole (Zalpa), that the milk- 
dentition might be very transitory. 
Recently Leche (7 & 9) has published the results of an inves- 
tigation concerning the relationships of the milk and permanent 
sets of teeth ina number of genera, adopting the more modern 
methods of microtomy to aid him in his researches, which were 
extended to foetal as well as numerous stages after birth, until the 
full adult dentition was acquired. 
In his first and prelimmary communication, Leche (7) came to 
the most interesting conclusion that in the anterior tooth-region 
of the adult Hrinaceus 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 Hrinaceus, 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 Hrinaceus possesses vestiges of two complete 
dentitions, and that those anterior teeth, which are apparently only 
