1916] Chandler: Structure of Feathers 329 
but the barbicels of the proximals of the outer vane are stouter and 
more irregular. 
Olor columbianus has the elongation of the ventral teeth of the 
distals less extreme, as in Anas, and has the hooklets even more 
slender than in typical ducks and geese. 
Speculum feathers occur in a very large number of genera, espe- 
cially of ducks, sometimes being white, but frequently some iridescent 
color, as blue, green, or violet, the structure in these cases being of 
the type described above for Anas platyrhynchos. A distal barbule 
from the brilliant green portion of a speculum feather of Nettion 
carolinense is shown in plate 21, figure 29b. The deep velvety black 
scapular feathers of Mareca, which are tinged with metallic green, 
have distal barbules in which the base as well as the pennulum takes 
part in the color effect (pl. 21, fig. 30a). 
c) Down 
The down barbules of all typical ducks are short, seldom over 1 
mm. long, and usually considerably less. They are simple and thread- 
like for the greater part of their length, but on the basal half of the 
barbs there are developed at the tip of the barbules 3 or 4, sometimes 
5, very conspicuous expanded nodes followed by a slender tip (pl. 35, 
fig. 104). On the outer portion of the barbs these enlarged nodes are 
reduced and there are a few terminal pairs of prongs taking their 
place. The number of terminal nodes differs to some extent in dif- 
ferent species, e. g., Anas has 2 or 38, Mareca 3 to 5, and Mergus 2 
to 4. In Branta there are 4 to 6, which are not so large and are 
farther separated. In Olor they are still more separated, less con- 
spicuous, and the transitional nodes on either side are better devel- 
oped (pl. 35, fig. 103). 
d) Relationships 
The feathers of the Anseres show high specialization in a num- 
ber of points of their microscopic morphology, and are unques- 
tionably to be regarded as the end of one line of evolution. The 
typical ducks show the specialized characters in their highest develop- 
ment, the geese, as represented by Branta and Chen, being lower in 
the scale, and the swans, as represented by Olor, still lower and form- 
ing a more or less natural bridge over the gap between the more 
typical Anseres on the one hand, and the Phoenicopteri on the other. 
