558 J; Tl WILSON AND J}; BP: HIGE. 
‘secondary adaptations ” which have operated amongst the 
marsupial group have resulted in the well-nigh complete ex- 
tinction of the successional dentition ? 
We have little doubt that the answer to these queries ulti- 
mately resolves itself into this,—that Kiikenthal has not been 
able to bring himself to question the validity of the prevalent 
judgment which has stamped mere secondary or residual laminar 
downgrowths—sometimes thickened marginally—as veritable 
enamel-germs of successional teeth. 
We are quite unable to sympathise with Kiikenthal’s final 
protest against Leche’s views as calculated “to disturb anew 
the now clear conception” of the dentitional problem. In 
our opinion Leche’s systematic criticism has been most timely, 
and if he has not gone the whole length in carrying out his 
criticisms to what we believe to be their logical conclusions, 
yet to him belongs the credit of having first introduced syste- 
matic critical criteria into the discussion of the developmental 
aspects of the problems of dentition. 
III. Serial Homology of the Molars. 
The question concerning the serial homology of the molars 
is not altogether separable from the fourth question, which 
deals with the origin of multicuspidate teeth in general. 
For a connected historical sketch of the state of opinion on 
these points we may simply refer the reader to Leche’s mono- 
graph (3, pp. 145-8). A succinct account may also be found 
in Woodward’s paper (14), and a more extended discussion of 
the subject in Schwalbe’s address (16). The principal views 
held may be shortly summarised as follows: : 
(a) The molars belong to the first or milk dentition (Owen, 
Beauregard, Kiikenthal [earlier view], Rose [earlier view], 
Osborn, Hoffmann, Leche). 
(2) The molars belong to the second or “replacing” denti- 
tion (Lataste, Magitot, Woodward). 
(c) The molars are not homologous to any single series, but 
to two or more dentitional series, either by actual fusion 
of the tooth-germs of the latter, or of the material from 
