164 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
The structure of the adult contour-feather does not differ much from that of the 
prepenna. The chief distinction—apart from size—whereby the two differ appears to 
be in this:—that in the adult the rami are arranged in pairs, and not alternately up 
the shaft; that the radii are confined solely to the rami, and do not grow along the 
shaft in the inter-ramal spaces ; and, thirdly, the rami are not so distinctly divisible into 
nodes and internodes; but there is not much difference in the form and length of 
the fila. 
Casuarius, Dromeus, and Apteryx all agree in that the prepenna has an elongated 
main shaft, and no distinct aftershaft. 
Rhea and Struthio agree one with another, and differ from the above-mentioned, in 
that the prepenna is umbelliform (P]. XLV. figs. 3, 3a). The main shaft appears to 
be represented by 3 rami conspicuously stronger than the rest with which they are 
associated. The prepenne are borne upon the tips of the definitive feathers for a very 
considerable time, giving a quite peculiar appearance to the first plumage. 
In Rhea the bases of all the rami, 9 in number, are seated around the upper 
umbilicus. The main axis of the feather—the rhachis—as just remarked, is represented 
by 3 elongated rami, bearing radii from the base upwards for a short distance, and 
produced beyond these into a long slender filament. The aftershaft is represented by 
some half-dozen rami, furnished with numerous delicate radii. These last are 
moderately long, strap-shaped filaments, with scarcely the faintest trace of fila. 
In Struthio the typical neossoptile (Pl. XLV. figs. 7, 7a) has the three rami repre- 
senting the main shaft produced far outward beyond the tip of the feather; the 
projecting region of each taking the form of a hardened, glistening, ribbon-shaped 
lamina, hollowed in its ventral surface. In this particular it closely agrees with the 
Crypturi. The radii are short, and run along the rami as a series of relatively broad, 
flattened, and pigmented lamine, set obliquely on to the ramus, and overlapping one 
another much as in the normal adult Meognathw contour-feather. Moreover, each 
radius bears numerous but small, probably degenerate, fila and hooklets. The forma- 
tion of the remarkable “ eye-spots” seen in these radii of many Neognathe are worthy 
of notice and further examination. 
The aftershaft rivals the main shaft in size, numbering some 12-15 rami, which do 
not, however, differ from those of the main shaft, save only in that the rami are not 
produced into elongated horny bands, whilst the radii are larger than those of the three 
rami representing the main shaft. 
