CH. II] MAMMALS AND ZOOLOGICAL REGIONS. 85 



ancient, the existing genera Pupa and Zonites going back 

 to Carboniferous times. 



Mr Wallace urges the superior claims of Mammals 

 upon whose distribution to found Zoological regions. He 

 thinks that they are best qualified " to exhibit by their 

 existing distribution the past changes and present physical 

 condition of the earth's surface." 



The reasons for this opinion are according to Mi- 

 Wallace the following: (1) They are dependent for 

 their means of dispersal upon continuity of land. At 

 least wide seas would be impassable. (2) They are (with 

 the exception of the bats which fly and might therefore be 

 subject to gales, and the mouse tribe which might be are 

 in fact conveyed in ships) too large to be carried acci- 

 dentally across seas which they could not traverse by 

 their own unaided efforts. (3) Again they are so highly 

 organised as to be largely independent of other animals : 

 though both purely carnivorous and purely vegetarian 

 forms exist there is for the most part no dependence 

 upon any particular kind of animal or plant as food, such 

 as we meet with for example among the insects. Or 

 where there is a restriction in the matter of diet as in the 

 case of the anteaters both of the old and new worlds the 

 food is universally found. (4) The mammalia form a group 

 which is fairly well known anatomically, we can therefore 

 form a tolerably correct judgment as to their mutual 

 relationships. That this is the case is shown by the 

 absence of any differences of opinion as to the outlines 

 of the main subdivisions of the family. (5) The last 

 argument favourable to the Mammalia is the fact that 



