CLASS AVES. 13 



number have moreover a small web between the ex- 

 ternal toes. 



The passerme birds include many more species than 

 all the other families ; but their organization is so 

 analogous that they cannot be separated, although 

 they vary gready in size and strength. Their two 

 external toes are united at the base, and sometimes 

 some way up their length. 



Finally, I have named (Grimpeurs) climbmg birds, 

 such as have the external toe behind like the thumb, 

 because the majority of them are formed for a vertical 

 position, to climb up the trunks of trees*. 



Each of these orders subdivides into families and 

 genera, principally by the conformation of the beak. 



* Since my first elementary table, I have thought proper to sup- 

 press the order picae of Linnseus, as it has no determined character. 

 M. Illiger has adopted this suppression. 



