1893.] Succession of the Teeth in Mammals. 497 
upper jaw, and the first three similar teeth of the lower jaw, 
also belong to the first dentition and have rudimentary 
successors. Therefore, excepting the last upper and lower 
molars which appear at a late stage of development, neither 
dentition of Didelphys belongs to the so-called permanent 
series. This opinion has been somewhat emended by Röse. 
Rosek’s RESEARCHES. 
MARSUPIALS. Dr. Rose gives the following summary of his 
principal results. “ When we combine the results of the fore- 
going researches, we find that the development of the teeth in 
the Marsupials follows exactly the same principle as that of 
man and the other mammalia. The first matrix is indicated 
by the dental fold, i.e. a part of the epithelium of the jaw 
which grows into the mesoderm aided by an extensive fold. 
Upon this dental fold are formed the dental caps which belong 
to the first series; in the case of Didelphys, the incisors, the 
canine, two premolars and the first molar. These dental caps 
are then immediately constricted off from the dental fold, and 
this ridge grows both inwards below the dental caps, and 
backwards behind the molar above mentioned. The posterior 
molars arise in exactly the same manner as I have described ; 
inthe case of man, through lateral extension of the dental 
e. 
“ While, however, in the case of man, the permanent ridge 
extends beneath the ten anterior teeth constituting the milk 
series and gives origin to ten permanent teeth, which cause 
their predecessors to be absorbed, in the Marsupials only the last 
premolar of the adult arises from the dental ridge of the per- 
manent teeth. It is nevertheless, more than probable that the 
. Outer (5th) incisors of Perameles, as well as of Macropus and 
Phalangista, are built up from the permanent ridge, i.e. they 
belong to the second dental series. The last upper premolar 
belonging to the second series in some cases simply pushes its 
. Way into a gap in the first series without causing the usual 
absorption of the first tooth in this row. This type we find to 
be shown in Didelphys, in Perameles, in Phalangista cookii, as 
