164 ME. W. P. PTCEAFT ON THE MOEPHOLOGT 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 

 sliaft 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, Drommis, and Apteryx all agree in that the prepenna has an elongated 

 main shaft, and no distinct aftershaft. 



Bhea and Struthio agree one with another, and differ from the above-mentioned, in 

 that the prepenna is umbelliform (PI. XLV. figs. 3, 3 a). The main shaft appears to 

 be represented by 3 rami conspicuously stronger than the rest with which they are 

 associated. The prepennse 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 (PI. XLV. figs, 7, 7 a) 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, liollowed 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 laminae, set obliquely on to the ramus, and overlapping one 

 another much as in the normal adult Neognathce contour-feather. Moreover, each 

 radius bears numerous but small, probably degenerate, fila and booklets. The forma- 

 tion of the remarkable " eye-spots " seen in these radii of many Neognathw 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. 



