80 
thesen der amerikanischen Palåontologen werden dadurch nicht be- 
ruibrt." (pag. 406). — But further the reptilian teeth exhibit some- 
times complications to be interpreted as a clustering (Scelidosaurus, 
Anthodon, Galesaurus a. 0.), they must have been formed by the 
uniting of several selachian teeth and probably this may be the 
case with all reptilian teeth. — The starting-point for the forma- 
tion of the teeth is the dentine tooth of the fishes; by coalescence 
of several of these is formed the reptilian tooth and through 
reiterated coalescence of these teeth the mammalian tooth is formed; 
the teeth of the three classes are thus not homologous, but repre- 
sent three stages in the tooth-evolution. ,,Damit ist zugleich der 
einfache mechanische Grund der allmåhligen Abnahme der Denti- 
tionen gegeben." (pag. 408). 
In the numerous papers of Råse from 1892 onwards ("Zur 
Phylogenie des Såugetiergebisses” a. 0.) the same theory is essen- 
tially set forth, supported by investigations of the embryonie devel- 
opment of the teeth. A multicuspid molar is not developed from 
a single dental papilla, but from just as many separate papillæ 
as the adult tooth has cusps; afterwards the enamel organ grows 
down like a cap around the summit.of the papillæ and unites them: 
»Die  Molaren der Såugetiere sind also entstanden durch Ver- 
wachsung mehrere einfacher, kegelfårmiger Zåhne zu einen kom- 
plicierten, hochdifferenzierten Zahngebilde.” (Phyl. d. Såugetgeb. 
pag. 625). We have — it is true — no certain palæontological 
evidence of that; though it must be remembered, ,,dass die Palå- 
ontologie lediglich in positiver Hinsicht beweiskråftig ist, niemals 
aber in negativer" (pag. 629); the assertion of the palæontologists that 
the origin of a true cusp can be traced back to a small basal 
knob is of no great significance, for it can be shown in the maår- 
supials that each of the basal knobs originates from its own sepa- 
rate papilla. The embryological positive evidence must weigh more 
heavily than the palæontological negative. — Of the reptilian teeth 
the unicuspid are certainly homologous with the fish-teeth, the 
multicuspid are homologous with the thekodont reptilian teeth- 
