138 K. BKOOM. 



relations in the triconodont type ; tig. 10 the reduction of 

 the anterior cusp and formation of an internal heel in the 

 upper, and the development of the small internal cusp in the 

 lower. Fig. 11 shows a later modification where there is a 

 -well-developed protocone and three external styles. The 

 lower molar has now a well-developed trigonid and two cusps 

 on the talonid. This is the type Avhicli is retained in 

 Dasvurus. Fig. 12 represents the last two upper and lower 

 molars of the Australian Native Cat, and shows the relations 

 of the upper and lower cusps. If these two molars be com- 

 pared with those of Chrysochloris, as shown in fig. 13, the 

 correspondence is so close as to leave little doubt as to the 

 general agreement of the main cusps at least. 



The cause of the loss of the postero-external triangle from 

 the upper molars of Chrysochloris is probably to be looked 

 for in the altered functions of the teeth. In normal insecti- 

 vorous and carnivorous types the teeth are crushing and 

 cutting instruments. In Chrysochloris, with the change of 

 diet from insects to worms, the teeth have come to be like the 

 reptilian teeth, mainly instruments of prehension. The various 

 species of Chrysochloris bite the worms, and may break 

 them into inch lengths, but they do not masticate them, and 

 very frequently quite entire worms are found in the stomachs. 

 In fact, C. hottentota appears to nearly completely lose its 

 teeth on reaching sexual maturity, and it certainly can live 

 quite satisfactorily without a single functional tooth in its 

 head. When the molars first ceased to be cutting teeth the 

 lower molar no longer needed to work against the iipper one 

 in front of it, and the large posterior cutting edge of the 

 molar disappeared. The lower molar then formed with the 

 upper ones behind each a biting arrangement, while the one 

 tooth overlapped the other. In the majority of species the 

 little talonid still meets the inner cusp, but in C. asiatica 

 and others all trace of the talonid is gone, and the teeth, in 

 biting, completely pass one another. 



