1916] Chandler: Structure of Feathers 315 
19, figure 19e. Unfortunately these two figures were reversed in 
position from the system usually followed in the preparation of 
the plates. 
c) Down 
The down of Steganopodes, like the pennaceous structure, is 
extremely variable. In Phalacocorax, Fregata, Pelecanus and Phaé- 
thon the downy barbules are of moderate length, i. e., from 1.0 to 
1.3 mm., and smoothly filamentous except in Pelecanws, which has 
minute prongs at the nodes on the distal portion of the barbules. 
In Plotus the downy barbules (pl. 34, fig. 99) are also filamentous, 
but are very long, frequently reaching a length of over 2 mm. Sula 
differs not only from other Steganopodes but also from all other 
birds in the enormous development of the prongs at the nodes. These 
reach a length of over 0.1 mm. in barbules which are only 0.6 to 0.8 
mm. long, being slender, filamentous, and frequently bifurcated 
(pl. 34, fig. 98). The only other birds which begin to approach Sula 
in the length of the prongs are albatrosses and puffins, and this might 
be looked upon as additional evidence of fairly close relationship 
between the Sulidae and the Procellariiformes. 
ad) Relationships 
The Steganopodes are a group of birds in which primitive char- 
acters are curiously combined with specialized characters, the result 
being a rather heterogeneous aggregation of more or less related 
forms which are specialized along different lines. They seem to 
fall into three fairly well-defined groups as follows: (1) Phalaco- 
corax, Fregata, Sula and Pelecanus; (2) Plotus; and (3) Phaé- 
thon. 
The first group may be regarded as containing the most typical 
Steganopodes, since they form the bulk of the group, and are 
least specialized. They seem undoubtedly to be derived from a 
primitive procellariiform type, and as certainly to stand at the 
base of the ciconiiform group, the next above them being the 
Ciconiae. 
The second group, including only the neotropical genus Plotus, 
though often grouped only as a sub-family of the Phalacocoracidae, 
differs very widely from the other Steganopodes in the structure 
of its feathers, in which it is very specialized. In some details of 
the feather morphology this genus shows such striking similarity 
