On the Rclationsliip of the Rodentia to the Marsupialia. 289 



XXX III. — On the Relationship of the Rodentia to the 

 Marsujyialia. By Dr. A. Fleisciimann *. 



The group of the Rodents incliules a great number of multi- 

 farious forms ; generally small and active animals, they are 

 able to adapt themselves to the most ditferent conditions of 

 existence over wide limits, and in consequence of the flexi- 

 bilUy 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. 

 ]t is remarkable that even then there were forms living in 

 great numbeis which have maintained their full power of 

 existence with but trifling clianges to the present day. In 

 the strata whicli furnish us with the knowledge of those 

 times, however, remaii?s 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 alone: ^vith 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 tiie 

 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 ' Sitzungsbericlite der konigl. Preussischen 

 Akademie der Wissenschaften zu Berlin,' March 20, 18i)0, pp. 299-305. 



