Discoveries in Mammalian Dentition. 311 



I do not quite understand wliy, merely on account of the 

 milk orii^in of tlie ]\rarsupial molars, Dr. Ktikeiithal saj'S of 

 the JMarsupials " 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-chano-inti; jiosterior teeth either of Placentals or ilar- 

 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 ]\Iarsupial posterior non- 

 changing teeth accentuates the right of the latter to bear the 

 name '' molar." 



Should, again, further research prove this to have been tiie 

 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 f, this brilliant 

 suggestion undoubtedly sheds a new light on the origin of 

 Cetacean teeth, and Dr. Kiikenthal may well be congratulated 

 on bis 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 tission 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 Embryonea von Spermophilus leptodactylus." 



t In the paper already referred to. 



