82 USE OF BIRDS FOB DEFINING REGIONS. [CH. II 



COLEOPTERA 



Upon what group then shall we found our divisions of 

 the earth's surface ? 



The great objection to the birds is that they can 

 fly and are therefore independent of most barriers ; with 

 them temperature, food and pre-occupation of the ground 

 must be the chief limitations to universal range. More- 

 over it will be remembered that this group contains the. 

 largest number of cosmopolitan genera and species. All 

 this tends to throw the claims of the birds into the 

 background. Against their exclusive use also is the fact 

 that they are a modern race, and would therefore at best 

 only indicate the present arrangement of land and sea. 

 At the furthest the birds go back to the Jurassic period ; 

 while the Carinate birds (speaking zoologically and not 

 etymologically) are not of greater age than the Tertiary 

 period. All curves of development show that birds are now 

 in the ascendant and that they have risen rapidly into 

 prominence. To this is due the variance of opinions 



