DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 571 
blance between the development of dp? and m+ in the early 
stages. Such resemblance as has been adverted to cannot, of 
course, by itself prove that an actual serial homology exists 
between the two teeth. It may indeed establish a prima facie 
case for such an homology. But, however we may decide the 
special problems of the distinctively marsupial dentition, the 
serial homology of the molars must remain as a general question 
of mammalian dentition, whose decision must yet be regarded 
as a separate and largely independent issue. 
The theories of molar homology set forth under (ce) and (d) on 
page 558 still remain to be dealt with. Of these the latter 
has not as yet been supported save by its author, and may, we 
believe, be regarded as a mere speculation. The former, which 
is supported by both Kiikenthal and Schwalbe, may best be 
discussed in connection with the next question, which primarily 
concerns the mode of origin of multicuspidate teeth, but which 
raises the general question of fusion of originally distinct 
dental units. 
lV. TuHeoriEs oF DENTAL FUSION AND THE ORIGIN OF 
MULTICUSPIDATE TEETH. 
The results of the present research do not, any more than 
Woodward’s, lend countenance to the view once advocated by 
Kikenthal, that molars are a result of the fusion of germs of 
more than one dentition, in the sense in which fusion has been 
supposed to occur between tooth-germs of the same series. 
But Kikenthal’s present position in regard to this question is 
rather less simply expressed. He holds “dass die echten 
Molaren im Wesentlichen zur ersten Dentition gehéren, dass 
sie aber ein Verschmelzungsproduct der Anlagen erster Denti- 
tion mit dem Material, aus dem sonst die zweite Dentition 
entsteht, darstellen ” (20, p. 112, and 27, p. 659). 
Against this view both Woodward (14, p. 447) and Leche 
(3, p. 146) have pointed out that it ignores the fact, upon 
which Kukenthal had himself insisted, that a residual dental 
lamina does normally develop by the lingual side of the first 
