PHYLOGENY QF THE PAL^OGNATH^ AND NEOGNATH^. 165 



The Structure and Homologies of the Adult and Nestling 

 Bemiges of Casuarius. 



The Nestling. — The youngest nestling in which these can be studied is that of a 

 stuffed C. casuarius salvadorii (Rothschild Mus.). 



In the dried wing of this there are 6 remiges. These are widely spaced, and 

 seated in a distinct posterior wing-membrane as in Neognathce. Each consists of a 

 moderately long calamus and a long and tapering rhachis bearing from 4-5 pairs of 

 symmetrically disposed rami set very far apart. There is but the feeblest trace of the 

 fusion between the prepenna and the displacing definitive feather now under discussion. 



In C. casuarius sclateri the growth ot the wing-spines has proceeded a stage farther. 

 The definitive feather is seen to bear rami as well as prepennae. 



In Casuarius lorice the quill-spines have grown very long and have lost the prepenna. 

 The 5th or innermost spine, representing the 3rd cubital remex, yet bears a few rami. 



In this stage, and in the last described (C. c. sclateri), we get an inkling into the 

 developmental history of these remarkable wing-spines. 



This is not the place for a recapitulation of the developmental history of a feather, 

 yet it would be well to recall one or two facts concerned with this for the better under- 

 standing of what is to follow. 



The axis of a feather, then, is divisible into two parts — the calamus or quill, and the 

 rhachis or shaft. The latter appeal's to be a continuation forwards of the dorsal region 

 of the tubular calamus. This being so, it is obvious that this drawn-out portion must 

 have two lateral free edges. These in the normal feather turn inwards towards the 

 middle line and finally meet, leaving a very fine seam to indicate the line of junction. 

 But the calamus, it will be remembered, is a thin, dense, horny, and semitransparent 

 structure and perfectly hollow, whilst the rhachis in section is solid, being composed of 

 an outer layer continuous with that of the calamus, and an inner, medullary portion or 

 pith — a white, soft, cellular structure resembling elder-pith. This pith seems to be 

 added for the sake of supporting the outer horny membrane, thus insuring lightness, 

 toughness, and strength. The whole forms the shaft. 



The dorsal elongated region of the shaft, now swollen out by pith, forms a sort of 

 plug to the otherwise open mouth of the calamus. The ventral edge of this mouth is 

 always visible. It forms the boundary of the upper umbilicus. 



The aftershaft, so conspicuous a feature in the feathers of the Cassowaries, represents 

 an elongation of the ventral region of the calamus exactly similar to that which obtains 

 on the dorsal. Thus we have a dorsal and ventral rhachis. 



In the remiges of C. lorice and C. c. sclateri we have only the dorsal rhachis, and 

 this is of great interest as only its outer layer is present, there being no pith-cells. 

 This layer takes the form of a delicate scroll-like, ribbon-shaped lamina whose free 

 edges turn inwards, but from the absence of the packing material, or pith, they fail to 

 meet in the middle line (PL XLV. fig. 14 a). 



vol. xv. — part v. No. 8.— December, 1900. 2 b 



