HISTORY OF THE KIWI. 



Carinatce 



Katitre 



The power of flight may be supposed* to have been acquired at the 

 point x. 



2. The earliest birds were able to fly : from them were descended 

 (a) the Carinate in which the power of flight was retained, and (b) 

 the Ratitffi in which it was lost in the course of evolution, the 

 assumption of a purely cursorial mode of life being accompanied by 

 degeneration of the wings and other parts connected with the 

 function of flight. This view is illustrated by the following diagram, 

 x again representing the point at which aerial progression began : — 



Carinatre 



Eatitre 



3. The third hypothesis is a modification of the second. It also 

 supposes that the earliest birds could fly and that the Eatitse arose 

 from these, their organs of flight becoming degenerate ; but instead 

 of supposing a single group to arise in this way and afterwards, by 

 divergence of characters, to split up into the various forms of Ratitaj 

 now existing, it assumes that each of these groups arose separately 

 from primitive flying birds. Thus while hypotheses (1) and (2) 

 ascribe a single or monophyletic origin to the Katite, hypothesis (3) 

 imagines them to have had a multiple or polyphyletic origin. The 

 following diagram — taken from Fiirbringer's elaborate " Stammbaum," 

 — expresses this theory, x having the same significance as before : — 



Carinata; 



Rhea 



Struthio 



Aptevyx 



