1893. Succession of the Teeth in Mammals. 495 
beneath them. Kükenthal refers these transformations in the 
dentition to natural selection, terminating with diminished 
calcification connected with the advantage of diminished spe- 
cific gravity. 
His general conclusions are, that all the earliest mammals 
were diphyodont. This is based upon his discovery of suc- 
cessional teeth in Marsupials, Edentates, Odontocetes and 
Mystacocetes. The monophyodont and homodont condition 
of many mammals, such as the toothed whales, he believes 
has been secondarily acquired. Within the higher members 
of the mammalian class the second dentition is developed 
progressively, both as regards form and funetion; while in 
` the lower divisions, the first or milk dentition is predominant. 
“Tn the rudimentary stage both dentitions are of equal value. 
Embryology gives us no support for the often expressed asser- 
tion, that one of the two dental rudiments has arisen in 
dependence upon the other. They are both sisters, whose 
mother is the simple invagination in the jaw, which we term 
the dental fold, (Zahnleiste.)” He continues, that there are no 
absolute differences between mammalian and reptilian teeth ; 
that not one of the characters of the mammalian teeth is 
perfectly constant, and that the derivation of the dentition of 
mammals from that of the reptiles does not appear to be too 
hazardous. Of the several series of teeth which are found in 
reptiles, only two persist in the mammals. 
From this I would dissent in part. The three differences 
between the mammalian and the reptilian teeth are shown in 
the capacity for the multiplication of cusps upon the crown, 
in the division of the fang whenever the crown becomes mul- 
ticuspid, in the acquisition of the cingulum. The frequent 
Succession of teeth in the reptiles, may be the cause of the 
non-progression of reptilian as compared with mammalian 
teeth. In the reptilia among the Theromorpha, we find true 
triconodont crowns, as for example in Galesaurus, and a 
heterodont dentition which closely imitates that of the 
Mammals; but the class differences appear in the fact 
that in the mammalia a development of lateral cusps upon 
the protocone, and the stages from the protodont toward the 
