DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES, 557 
But it is extremely difficult to follow Kikenthal in his ex- 
planation of the manner in which suppression has_ been 
brought about in different groups. He first formulates a 
“law of reduction,” stipulating that the tendency to sup- 
pression has constantly affected the first dentition most 
strongly. Thus he explains the suppression of the supposed 
“ prelacteal” series. So far all is intelligible. But when he 
comes to explain suppression as witnessed within the mamma- 
lian class itself the case is much ess clear. ‘ Bei den nie- 
deren Sdugetieren dominirt die erste Dentition, die zweite 
kann wohl ausgebildet sein (Edentaten),! oder aber sie fallt 
aus besonderen Griinden-—secundaren Anpassungena—dem 
Rudimentarwerden anheim (Beutler, Cetaceen).? Bei den 
hdheren Saugetieren verliert die erste Dentition an Bedeutung, 
und die zweite kommt mehr zur Geltung. Wenn jetzt gewisse 
Lebensbedingungen einen Zahnwechsel ungiinstig sind, wird 
nicht die zweite Dentition unterdritickt werden, sondern die 
erste eine raschere Entwickelung und ein fritheres Ende 
nehmen.” (The last sentence expresses the corollary from the 
previously enunciated “law of reduction,” and formulates 
precisely what we believe to have happened in the case of 
Marsupials.) 
In view of this startling exception of Marsupials from the 
ordinary operation of the law of reduction, it is rather 
strange to find Kukenthal going on at once to say that “ein 
einheitliches Gesetz beherrscht also die Dentitionen aller 
Wirbeltiere ” (p. 657). But why should Kikenthal ask us to 
make a special exception of the Marsupials from the operation 
of his own “law”? Why should he expect us to assent to 
the idea that while ‘‘ conditions of life unfavorable to tooth- 
change,” amongst mammals generally, should tend towards 
suppression of the milk dentition, yet nevertheless the 
? Upon this statement with regard to the Edentata, as well as upon the 
entire passage, Leche’s rejoinder (28, p. 275) may be consulted. 
2 We are constrained to avoid special discussion of the Cetacean condition 
because we are disposed to hold with Leche that the homology of the persis- 
tent teeth of Cetacea must still be left as an open question (28, pp. 274-6). 
