1916] Chandler: Structure of Feathers 295 
c) Summary 
In addition to the common ratite characters, Apterygiformes 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 
eroup. 
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. Im 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. 
