INTRODUCTORY 9 



as an aftershaft (hyporhachis). This is a duplicaturc of the 

 main shaft, but much smaller and more delicate, and springs 

 from the upper umbilicus of the main shaft. In the Game- 

 birds it is especially well developed, while in others it is 

 reduced to a mere vestige, or is wanting altogether. In the 

 great feathers which form the "quill" or "flight" feathers 

 {remiges) of the wing, and in the tail feathers {rectrices) the 

 after shaft is invariably wanting. Among the Ostrich tribe it 

 is present only in the Emus and Cassowaries, and here it is of 

 great size, as large indeed as the main shaft. 



The contour feathers of the Ostrich tribe — save only in the 

 Tinamous — it may be remarked, are peculiar in that their vanes 

 are not held together to form a well-knit " web," the radii being 

 degenerate, and failing to hold the vanes together ; hence these 

 vanes are said to be "discontinuous". 



Down feathers differ from contour feathers in that the barbs, 

 or rami, of the feathers are of great length and slenderness, and 

 often all arise from a common base — the top of the calamus, 

 instead of being ranged along each side of a long rhachis. The 

 radii (barbules) of such feathers are represented by mere 

 filaments, or sometimes by nodular swellings, which again may 

 assume a pyramidal form. 



As touching "filo-plumes" little is known' as to their mean- 

 ing or purpose. There are the long hair-like threads which 

 remain sparsely distributed over the body of a fowl when 

 plucked. They grow in clusters of five or six, or more, about 

 the bases of the contour feathers, and when examined micro- 

 scopically are found to consist of a simple, solid axis, terminating 

 in a few weak barbs and barbules. An examination of the late 

 stages of growth, just before development is complete, however, 

 shows that these are degenerate feathers, inasmuch as there 

 will then be found a considerable number of barbs, arranged 

 much after the fashion of the barbs of a down feather. Among 

 these one will be found stronger than the rest, and this 

 eventually is left, the rest disappearing. In some birds these 

 filo-plumes play a conspicuous part in the coloration of the 

 surface of the body, since in such cases they attain a great 

 length, and develop relatively large vanes. These project 

 beyond the level of the contour feathers and may form large 

 white patches, as in the thigh patches of the Cormorants, or 



