of tlie Tooth- Rudiments in Rodents. 305 



adopting- Baunie's view we avoid a difficulty of the following 

 kind : if we derive continuously growing rootless teeth from 

 rooted teeth with limited growth, we are compelled to assume 

 a repetition of the same process (convergence) in represen- 

 tatives of the most widely different families, which have no 

 direct connexion whatever one with another ; for, according 

 to Baume, we find continuously growing teeth " in a motley 

 series among the Carnivora, Cetacea, Prosimi^e, Multiungu- 

 lata, Sirenia, Ruminantia, Rodentia, and JMarsupiaiia. They 

 are, as appears from the above comparison, widely distributed, 

 but also very scattered, when relationships are considered. 

 The various representatives occupy a number of isolated 

 positions." 



Mahn * and Fleischmann have disputed the justice of 

 Baume's assumptions, adducing weighty arguments in oppo- 

 sition to them. 



Moreover this conception of Baume's is in accordance with 

 the other peculiar views advanced by this author, the most 

 prominent of which is his theory that the milk-teeth should 

 not be regarded as constituting a special dentition. Accord- 

 ing to this idea we should only get a pseudo-diphyodontism 

 in Mammals. The milk-teeth would belong to the same 

 series as the permanent ones ; they would merely be feebler 

 structures, developing more quickly. The stronger (perma- 

 nent) teeth develop more slowly according to Baume, but 

 afterwards displace the quickly developed feeble (milk-) teeth. 

 This is not the place for the elucidation of the question as to 

 what are the facts of comparative anatomy and embryology 

 upon which Baume bases his conception. I still have to 

 refer incidentally in the special portion of this paper to the 

 results of Baume's investigations into ontogeny. At any 

 rate, even Baume coincides with all other authors in assuming 

 that the dentition of the Bodentia has arisen by means of 

 reduction from a richer and completer series of teeth. 



How extensive the reduction must be supposed to have 

 been is evident from a comparison of the existing dental 

 equipment of the Rodents with the fundamental type of the 

 dentition of the Eutheria, as the latter is formulated by 

 Schlosser j after Oldfield Thomas. According to the theory 

 referred to, the ancestors of the Placentalia would hav^e 

 possessed live incisors, one canine, four premolars, and four 

 molars, though it must certainly be remarked that such an 



• R. Mahn, " Bau und Entwicklung der Molareu bei Mus und Arvi- 

 cola,'" Moqjhol. Jahrb. Bd. xvi. Ileft 4. 



t M. Schlosser, " Ueber die Deutung des Milchgebisses der Sauge- 

 thiere," Biol. Ceutialbl. Bd. x. 



