488 A CX3NTRIBUTI0N TOWARDS OUR KNOWLEDGE OF 



V. Structure of the Feathers, axd the nature of the Nestling Plumage. 



Contour feathers : the structure of the adult contour feathers calls for no special 

 remark, all the feathers of the trunk possessing a normal, well-knit, coherent vexillura. 

 This fact, however, afifords a valuable and important standard of comparison between 

 the contour feathers of the adult and those of the nestling, and brings out one very 

 interesting point of difference between these two stages. 



The plumage of the newly-hatched Megapode will probably prove to be unique. 

 It differs from the definitive contour feathers of the adult on the one hand, and the 

 typical pre-pennffi, which precede these, on the other. It agrees very closely ^\-ith 

 that recently described by me (11) in the nestling Owl; in that, like this, the trunk 

 feathers are of a loose, semiplumous character, the vesillum of the feathers being 

 disconnected. 



By a typical pre-penna, I should e.-cplain, that I take as my standard of comparison 

 the pre-penna of the strictly Gallinaceous birds, e.g. Turkey (PI. XLIX, Fig. .5). In 

 this we have, microscopically examined, a distinct main-shaft, and an after-shaft, each 

 provided with rami and radii; the latter bearing feeble fila (Fig. 11 F.). The 

 after-shaft breaks up at once into rami, whilst in the main-shaft the rhachis is 

 traceable upwards for a considerable distance. 



A feather, taken from the same region of the body of a ripe embryo or of a 

 newly-hatched Megapode chick, shows a distinct advance upon this. As will be seen 

 in the figure (Fig. 6) the main-shaft is long and tapering, and bears numerous 

 bilaterally arranged rami ; the after-shaft likewise is well defined, and bears rami 

 disposed as in the main-shaft Furthermore, the rami and radii differ slightly in 

 structure. 



In the Turkey the rami were produced into fine terminal filaments beyond the 

 last pair of radii, and the radii were seen to be provided only with feebly developed 

 fila; this was the case no matter what part of the feather was examined. 



In the Megapode the rami and radii, as in the more perfect contour feathers, 

 differ somewhat in structure according to whether those examined are at the base 

 or the tip of the feather. The rami from the base are long, and slender, and 

 the radii take the form of long delicate rods bearing more or less well-marked nodal 

 swellings or flanges at intervals (Fig. 10), which may be produced forwards into fila. The 

 rami, from the distal end — of the main-shaft only — resemble rather those of the pre- 

 pennae of the young Tinamou which I described some time since (11), inasmuch as each 

 ramus is laterally compressed at the base into a blade-like lamina, which, tapering 

 forwards, gradually becomes segmented and rod-shaped; the fila are here constant, paired, 

 and proceed from the distal end of each segment. These fila are the homologues 

 of the " booklets " of the more perfectly developed contour feathers : indeed, booklets 

 occur, though feeble, in the feather from which this description is taken. The nestling 

 down feather of the Megapode, however, differs from that of the Tinamou chiefly in 

 that the rami are somewhat weaker. 



In spite of this resemblance between the nestling down plumage of the Tinamou 

 and the Megapode, there can be no doubt that the feathers composing each differ in 



