1916] Chandler: Structure of Feathers 295 



c) Summary 



In addition to the common ratite characters, Apterygi formes are 

 characterized by: 



(1) The presence of small apteria; 



(2) No specialized remiges or rectrices; 



(3) No aftershaft; 



(4) Feathers broad and tapering, outer part of barbs naked 

 towards tip of feather; 



(5) Barbules of typical downy type, smooth and filamentous, 

 or with distinct nodes and prongs on pennulum, the base small but 

 well-formed. 



5. SUMMARY OF RATITAE 



Based on epiphyology the Ratitae are divisible into two main 

 groups, the Struthioniformes and Rheiformes on the one hand, the 

 Casuariiformes and Apterygiformes on the other. All of them 

 agree in the absence or rudimentary condition of the apteria, the 

 uselessness of the remiges for flight, the absence of differentiated 

 plumules and filoplumes, and the lack of any typical pennaceous 

 structure. 



The first group seems to represent two branches of an early 

 offshoot from the stem leading to carinate birds, the type of feather 

 structure being at the end of a short path of evolution, the barbules in 

 both cases differing from either a pennaceous or downy type, but 

 apparently not leading to either. The aftershaft is absent in this 

 group. 



The second group seems to represent two branches of another but 

 possibly later offshoot from the carinate stem, the barbules being of 

 typical downy type, and resembling, especially in Casuariiformes, 

 the down barbules of penguins and of the neossoptiles of many 

 other forms of water birds. In the Casuariiformes the aftershaft 

 is equivalent to the main feather plate ; in Apterygiformes it is 

 absent. In the latter group small lateral apteria are present, but 

 there is as much reason to believe them to be just developing as to 

 look upon them as vestigial. 



