of the TootTi-Biidtments in Rodents. 303 



represented by the Marsupialia ; on the otlier many conditions 

 of form are approximated to tlie type of the higher Placen- 

 talia. The Rodents stand as it were as ancient monuments 

 of a time which has long since disappeared, and unfold before 

 us the representation of the modification which, perhaps as 

 early as the Cretaceous period, elevated the Protheria into 

 the condition of placental Mammals. Nevertheless the facts 

 with which we are at present acquainted do not suffice to 

 prove a direct relationship to the Marsupials. It is only 

 possible to maintain that animals very similar in their organi- 

 zation to the structure of the Marsupialia were the ancestors of 

 the Eodents. The forms of phylogenetic importance are not 

 concentrated in one group, but are distributed over all four 

 divisions of the Rodentia ; for, in accordance with the special 

 conditions of existence, with which we are still very imper- 

 fectly acquainted, certain organs have retained their primitive 

 characters in one division, and others in another." In direct 

 reference to our results in the case of Lepus I would also like 

 to quote here the concluding sentence of the same chapter : — 

 "As regards the Lagomorpha, it seems to me that the theory 

 founded by Schlosser is established, namely that they did not 

 branch off from the primitive stock simultaneously with the 

 true Rodents, but that they have existed as placental Rodents 

 only for a relatively short period." 



In other respects Schlosser's admirable palasontological 

 and general investigations * upon the organization and 

 historical development of the Rodents have already been 

 exhaustively discussed in Fleischmann's treatise. 



Especial stress must also be laid upon the fact that, 

 although ceitain of the herbivorous Marsupials possess a 

 dentition which is in the highest degree similar to that of the 

 Rodents [Phascolomys even has continuously growing incisorSj 

 and withal the dental formula i. j, c. q, p. ^, m. ^), Fleisch- 

 mann nevertheless expresses himself very decidedly against 

 a direct derivation of the Rodents from these animals. He 

 writes : — " The herbivorous Marsupials do not stand in a 

 closer phylogenetic relation to the Rodents, but are a pecu- 

 liarly differentiated branch of the Metatheria. My object in 

 minutely describing the dentition of various Marsupialia was 

 merely to demonstrate that the reduction of an originally 

 complete dentition in the herbivorous Diprotodontia occasions 

 arrangements which are very similar to the dentition of the 



* M. Schlosser, " Die Nager des europaischen Tertiars nebst Betraclit- 

 nngen liber die Organisation und die geschichtliche Entwicklung der 

 Nager iiberhaupt " : Cassel, 1885. * Paleeontographica/ 31 Bd. Dritte 

 Folge, 7 Bd. 



22* 



