i60 NATURAL SCIENCE. Sept., 



described as being thrust down between them ; and the formation of 

 comparatively deep channels by the approximation of their lower 

 edges. These channels are not maintained far, if at all, past the most 

 proximal hooklet ; from this point, it will be seen, these sectionised 

 radii diminish in size, terminating close against the surface of the 

 next ramus.' Now it only remains for the reader to draw upon his 

 imagination, to see at once that a comparatively severe strain would 

 have to be exerted upon the rami to pull them apart, and if he will 

 only make the experiment on some large quill feather, he will 

 be amply satisfied ; then let him sever a few rami at their base, and 

 see how easy it is to separate them by pulling the ends in opposite 

 directions, the booklets, of course, gliding along the grooved edges. 



Now a word as to the " warping." The radii of both distal and 

 proximal series are, it will be remembered, longitudinally curved, or 

 " warped," as I have termed it, but in Fig. 2 the radii have the 

 appearance of flattened not curved laminae ! How is this ? Well, I 

 have chosen to give the appearance they present under the microscope 

 when seen in sitii, rather than avail myself of the licence allowed me 

 in adopting a semi-diagrammatic figure, for the sake of those who 

 take up this work for the first time ; for unless seen in section, it is 

 difficult, if not impossible, to consider these anything but what they 

 appear — flattened lamellae, seated obliquely along the ramus, and even 

 examination under high powers does not reveal the true state of 

 things. Their actual form appears in section as in Fig. 5, which 

 represents three radii cut off close to their base. 



As touching the " channels " of the proximal series, what we 

 have now to do is not so much to tender a reason for their forma- 

 tion — this being rather too presumptuous, as to offer a suggestion to 

 that end. The first thing that will occur to the thoughtful reader is, 

 if these edges were free, and directed straight downwards, might they 

 not be a source of danger to the booklets, inasmuch as the latter 

 would perhaps frequently catch their lower instead of their upper 

 edges ; while the present arrangement suggests a twofold purpose : 

 firstly, to afford a wind-proof surface for the downstroke of the wing 

 (in the case of the remiges and flight feathers), thus preventing the 

 displacement of the booklets by the upward rush of air; and, secondly, 

 to conduce to that marvellous elasticity of the feather we paused to 

 admire in the earlier part of this paper, the booklets gliding freely 

 over the smooth, hollow surface, yet with difficulty letting go their 

 hold. Surely, there seems to be good reason for these views. At 

 any rate, just such an interpretation as this seems to find favour with 

 so good an authority as Dr. Gadow. 1 find on reference to his most 

 valuable work the following remarks, which, by the way, however, 



1 These diminished portions, it should be noted, are the distal ends of radii 

 arising nearer the proximal end of the ramus. A moment's reflection will show — 

 bearing in mind their oblique direction — how, that being placed one in front of the 

 other, the sections will gradually decrease. 



