PALEONTOLOGY SINCE CUVIEE. 51 



origin of the Mammalia as far back as the Trias at 

 least, and probably even further back, but we have 

 to assume that the class was one of pretty consider- 

 able extent. And, with the beginning of the 

 Tertiary period we already stand on the threshold 

 of the present. Whether or not there was ever a 

 Sahara ocean, 1 or Europe ever half under water or 

 encrusted with ice, or England torn away from 

 the mainland by an inroad of the sea, or again 

 whether or not North Africa could exchange land 

 animals with South Europe by means of two 

 isthmuses these and other incidents on a grand 

 scale would in no way affect the truth of an 

 uninterrupted development. There remain, it is 

 true, a series of animo-geographical problems un- 

 solved, problems which are geological as well ; for 

 instance, the case of Madagascar, the distribution 

 of wingless birds, the Edentata, the isolated cases 

 of the Australian fauna, &c. These difficulties 

 must simply be accepted as such. They do not 

 hinder our recognising the natural connection of 

 the living world which is forced upon us by other 

 facts, and they do not oppose our present concep- 

 tion of the universe, which is already a very old 



1 This conjecture may be said to be altogether refuted by the 

 latest investigations. 



E 2 



