THE CARINATE OR KEEL-BREASTED BIRDS 3s 



To-day, as a result, we find Diving-birds and Tree- climbers, 

 Hawks and Long-legged Waders, and so on. 



These different kinds of birds we group together in different 

 assemblages, which are known as " Orders," and these are further 

 sub-divided into Sub-orders, Families, and Genera, till finally we 

 come to species. In this way we can sort out and bracket together 

 all birds according to their relationship one to another. 



While some Orders are made up of birds which have retained a 

 relatively large number of archaic characters, and hence are said 

 to be primitive, others have changed their structure very con- 

 siderably, showing many signs of descent from more modified, 

 more changed forms, and these are accordingly to be regarded as 

 higher in the scale of evolution. We shall endeavour to express 

 these degrees of development by working upwards from the lowest, 

 or more primitive, types to the highest, or latest evolved forms. 

 The lowest of all, the Ostrich tribe, we have already surveyed. The 

 remaining types are now to be traced out. 



