1896. ] MAMMALIAN DENTITION. 591 
compose the order Insectivora, we find a considerable variation in 
their dentition, both as regards the number of their teeth and the 
specialization of the individual members of the dental series. 
Thus in Gymnura and Talpa we find in the adult the full pla- 
cental dentition of 44 teeth, while in two Shrews (Diplomesodon 
and Anurosorex) the dentition is reduced to 26 teeth, other families 
presenting numerous stages intermediate between these two. If 
primitive, the supposed presence of 4 upper incisiors in Sorea and 
the 4 upper molars of Centetes must be of great interest, but the 
former I believe is capable of being interpreted differently, and the 
latter to be a secondary character. 
A closer examination of these dental variations shows that they 
can be grouped under four heads :— 
(1) A tendency for a suppression of the 3rd incisor above and 
below, di. 3 disappearing first. 
(2) A suppression in the premolar series, pm. 1 in the Cen- 
tetide, pm. 2 in Selenodon. 
(3) A suppression of the posterior molars, the number vary- 
ing trom 4 to 3, the normal 1umber being 3. 
(4) A tendency for reduction in the functional importance of 
the milk dentition. 
Although representatives of only 5 out of the 9 families of the 
Insectivora (Flower and Lydekker, 4) have been systematically 
examined, this last variation is so marked, that one is forced to the 
conclusion that the order as a whole is tending to lose its milk- 
teeth. 
Among the forms examined, probably only Hriculus and Echinops 
possess the same number of functional milk and permanent 
antemolar teeth, but these forms have already a reduced dentition. 
Of those provided with 44 teeth, viz. Gymnura and Talpa, we find 
di. 3, dpm. 2 
dpm. 2 
omitting the 1st premolar, all the remaining milk-teeth are reduced 
and though cutting the gum can hardly function (if at all) for 
more than a week or two. 
The remaining genera examined show this reduction in a varying 
degree, the maximum being attained in Sorew, where in all 
probability the entire milk series is reduced and functionless. 
If then it be a fact, as is now generally believed, that the milk 
dentition preponderates in the early Mammalia and in the living 
Marsupials, then we must come to the conclusion that the living 
Insectivora are specialized forms tending towards a Monophyodont 
condition in which the preponderating dentition is the replacing 
or permanent set. 
in the former reduced and functionless, while in Z'a/pa, 
List oF REFERENCES. 
1. Barn, S.—‘‘On the Dentition in the Mole.” Trans. Odont. 
Soc. 1865-67, p. 261. 
la. Braanpr, E—Ueber d. Zahnformel der Spitzmause. St. 
Petersburg, 1878. 
