On the Relationship of the Rodentia to the Marsupialia. 289 
XXXIII. — On the Relationship of the Rodentia to the 
Marsupialia. By Dr. A. Fleischmann *. 
The group of the Rodents includes a great number of multi- 
farious forms ; generally small and active animals, they are 
able to adapt themselves to the most different conditions of 
existence over wide limits, and in consequence of the flexi- 
bility of their requirements they people the surface of our 
planet in astonishing quantity. Their palaeontological range 
extends back to the commencement of the Tertiary period. 
It is remarkable that even then there were forms living in 
great numbers which have maintained their full power of 
existence with but trifling changes to the present day. In 
the strata which furnish us with the knowledge of those 
times, however, remains of gigantic Rodents are preserved 
which flourished side by side with smaller allied forms, but 
owing to unfavourable conditions soon disappeared again. 
Now we have along with families of almost universal distri- 
bution others whose dwelling-places are limited to particular 
regions, and the last giant among the Rodents, the Gapy - 
hara , leads a solitary existence in the marshy plains of the 
South-American rivers. 
It might be thought that a group of animals with a history 
extending so far back in time and showing such remarkable 
conditions of geographical distribution and so elegant a bodily 
structure would have induced many naturalists to come for- 
ward as its historiographers. But from the study of the lite- 
rature this expectation appears to be a deceptive one. 
It is true that we can cite abundance of works upon the 
systematic arrangement of this class and the relationship of 
the different species and families founded upon the structure 
of the teeth. If we‘ leave out of the account the special 
researches which have been made upon the typical experi- 
ment-animals of our laboratories, the guinea-pig and the 
rabbit, anatomical investigations upon the constitution of the 
different systems of organs have been, since the time of 
Pallas, very rarely extended to the whole group. And if the 
knowledge of the soft parts must be characterized as quite 
unsatisfactory, the want of works on the phylogenetic history 
of these animals is still more to be regretted. 
Leaving out of consideration the various attempts to refer 
the Rodents to a certain place in the system, we have here to 
* Translated from the ( Sitzungsberichte der konigl. Preussischen 
Akademie der Wissenschaften zu Berlin/ March 20, 1890, pp. 299-305. 
