290 Dr. A. Fleisclimann on the Relationship 



cite only a work of M. Sclilosser's ' On the Rodents of the 

 European Tertiary, with Considerations npon the Organiza- 

 tion and Developmental History of the Rodents in general " 

 (' Paleeontographica,' Bd. xxxi.). Schlosser is the first and 

 only naturalist who, from the standpoint of the modern 

 theory of evolution, has submitted the palajontological remains 

 of the animals in question to a remarkably thoroughgoing 

 treatment, and then made an attempt at a phylogenetic 

 arrangement under close consideration of the skeletal and 

 dental structure of the recent forms. Deductions from very 

 numerous facts led him to the hypothesis that the Rodentia 

 are directly related to the Marsupials. From my own inves- 

 tigations I regard this conception as quite irrefutable ; but 

 unfortunately Schlosser was led, half a year after the publi- 

 cation of his exemplary work, to recall his fine demonstrations 

 and even to characterize them as untenable. 



Since that time the question has rested completely, for, 

 owing to the little sympathy that many zoologists have with 

 palfeontological results, Schlosser's work appears to have 

 become known only to a few. 



By some investigations in developmental history I was 

 led several years ago to give more attention to the question 

 of the genealogical relationships existing between the different 

 classes of Mammalia, and I now venture to put forward a 

 brief report upon the results at which I have arrived with 

 respect to the Rodentia. 



As the relationship of the Mammalia is determined cus- 

 tomarily by the nature and number of the teeth, I will com- 

 mence my statement with the dentition of the Rodents. The 

 remarkable parallel in dentition between Marsupialia and 

 Rodentia has already been repeatedly dwelt upon without any 

 careful inquiry whether we have here a mere analogy or an 

 actual homology indicative of direct relationship. The course 

 of conversion, according to my observations, which agree 

 well with previous statements, may be traced from the 

 kangaroo-like Marsupials to the true Rodents, the analogous 

 lateral branches of Phalangista and Phascolomys furnishing 

 opportune evidence of the former intermediate forms. The 

 dentition of Phalangista vulpina shows in the upper jaw two 

 canines and six incisors, of which the middle ones are the 

 largest, the lateral the smallest. In the lower jaw there are 

 two large chisel-shaped incisors, the alveoli of which extend 

 as far as to the first molar. Behind the two large incisors 

 there are four smaller ones ; there are therefore six incisors 

 in the lower jaw, diminishing in size posteriorly, so that the 

 third pair appears only in the form of very diminutive points 



