290 Dr. A. Fleischmann on the Relationship 
cite only a work of M. Schlosser’s c On the Rodents of the 
European Tertiary, with Considerations upon the Organiza- 
tion and Developmental History of the Rodents in general ” 
Palseontographica,’ Bd. xxxi.). Schlosser is the first and 
only naturalist who, from the standpoint of the modern 
theory of evolution, has submitted the palaeontological 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 
palaeontological 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 wdiich 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 
