Discoveries in Mammalian Dentition. it 
I do not quite understand why, merely on account of the 
milk origin of the Marsupial molars, Dr. Kiikenthal says of 
the Marsupials ‘there are no molars at all, but premolars,” 
for the words molar and premolar in no way imply either 
difference or identity of series, and the “ molars” are simply 
the non-changing posterior teeth either of Placentals or Mar- 
supials, whether homologized with the milk or permanent 
series. In fact if the Placental molars are also of milk origin 
their complete homology with the Marsupial posterior non- 
changing teeth accentuates the right of the latter to bear the 
name ‘ molar.”’ 
Should, again, further research prove this to have been the 
origin of the Placental molars, Dr. Kiikenthal’s extraordinary 
and, to all appearance, most unlikely theory as to the fusion 
of teeth of the permanent and milk sets in order to form the 
molars will fall to the ground *. 
Of other interesting points in Dr. Kiikenthal’s papers a 
reference may be made to his theory as to the production by 
fission of the many simple unicuspid teeth of Cetacea out of 
compound multicuspid teeth, such as are found in other 
Mammals. Combined with the fact that real congenital 
fission does occasionally take place in Seals and other 
Mammals, as pointed out by Mr. Bateson t, this brilliant 
suggestion undoubtedly sheds a new light on the origin of 
Cetacean teeth, and Dr. Kiikenthal may well be congratulated 
on his clever interpretation of the facts. At the same time 
his ideas on analogy and methods of evolution would appear 
to be somewhat peculiar when he describes as analogous to 
such a congenital fission the common mechanical wearing down 
of a seal’s teeth to the roots, whence by the loss of the crown 
two “teeth” are formed out of each one. Such a multipli- 
cation of teeth may occur in any rooted-toothed animal if it 
only live long enough, and can hardly be considered more 
“analogous ”’ to true fission than the cleavage of a man’s jaw 
by a battle-axe is analogous to hare-lip. 
Another way, and one perhaps more probable, by which 
Cetaceans may have obtained their numerous teeth is also 
rendered possible by Dr. Kiikenthal’s observations on their 
embryology. Instead of trusting to the comparatively rarely 
occurring fission, the ordinary process of hypsodontism 
applied to narrow multicuspid teeth, such as those of certain 
* For all evidence as to this remarkable suggestion we have the mere 
statement ‘‘ Beim ersten Molaren ist dies oft noch deutlich nachweisbar, 
besonders schon z. B. an Embryonen von Spermophilus leptodactylus.” 
+ In the paper already referred to. 
