938 "The American Naturalist. [November, 
tributions to the histories of both these orders, while other problems 
remain open. 
In the paper of about 1060 pages now before us, M. Ameghino gives 
his views on the general subject. It seems that in his work Filogenia, 
published in 1884, he adopted the view of Gaudry of 1878, (previously 
barely suggested by others), that complex teeth of Mammalia are pro- 
duced by the fusion of a number of originally distinct simple teeth; a 
- view which has been supported by Kükenthal and Röse on embryologic 
grounds. It had been previously believed that additional cusps are the 
product of plications of the dental crowns of simple teeth, and in 1873 
and later I had constructed on that basis a phylogenetic system of 
- dentition. This, as is well-known, proceeds from the simple to the 
complex, without the element of fusion entering at any point. The 
series is, for the upper jaw; the haplodont, triconodont, tritubercular,’ 
(sectorial) quadritubercular, quinque- and sextubercular, and the 
various lophodont forms; for the lower jaw; haplodont, triconodont, 
tritubercular, tuberculosectorial, (sectorial), quadritubercular, and the 
various lophodonts. This succession corresponds with the time order 
both in North America and Europe, and it is to be supposed that it 
must, therefore, do so in other parts of the earth, wherever the Mam- 
' malia have developed a dentition beyond primitive types. 
I have never attempted to bring into this system the Monotrematous 
‘Prototheria, and have maintained that they constitute a distinct 
phylum’ My discovery that the dentition of the Permian Cotylo- 
saurian family of the Pariotichide consists of simple teeth arranged in 
transverse series,* induced me to remark’ “ that the only question that 
could arise” as to the hypothesis of dental fusion “is with regard to the 
Multituberculata.” A fusion of the teeth of the Pariotichide could 
_ produce molars like those of the Multituberculata ; but there is no evi- 
dence that such a fusion has ever occurr 
Returning to the Eutherian Mannada, we observe that Ameghino 
believes that the complex molars have preceded the simple ones in the 
_ order of time, and that the tritubercular molar is the result of a loss of 
a tubercle of the quadritubercular; the quadritubercular the result of 
* Riitimeyer used the term trigonodont for triangular molars, without specifica- 
tion of the number of tubercles. This word cannot take the place of tritubercular, 
_ since the evolution is a question of tubercles, and not of shape. Some trituber- 
cular teeth are quadrangular (Periptychus) and vice versa. 
~  $See Amer. Journal of Morphology, 1889, p. 146. 
* Proceeds. Amer. Philos. Society, 1895, 439-444, 
5 Primary Factors of Organic Evolution, 1896, p. 334. Amer. NATURALIST, 
1896, Plate VIIa, p. 801. 
