356 Mr. W. P. Pycraft on the 



extend beyond the most distal radii. Under a high power 

 of the microscope (PI. XI. fig. 6) the radii are seen to be 

 composed of a series of flat lamellae, or strap-shaped rods, 

 joined end to end, and decreasing from the base upwards ; 

 the tipper and lower margin of each radial segment are 

 produced into a very delicate filum* or thread. These fila 

 decrease in length towards the tip of the radius. The radii 

 are of a nut-brown colour, the pigment being distributed 

 in granules. 



Plumulce. — The plumulse — the true nestling-down in this 

 case — which develop towards the end of the nestling period, 

 differ from the neossoptiles in that the rami are more 

 numerous, forming thick brush-like tufts, and are not far 

 produced beyond the radii. Microscopically the radii are 

 found to be longer than in the adult plumulse, and fila 

 occur sporadically and rarely. 



Rhamphotheca. — The cone-shaped elevations on the inside 

 of the rhamphotheca described in the adult (p. 352) can be 

 traced in all the nestlings, but not without difficulty in 

 stages 1 and 2. 



IV. Pterylosis of the Embryo. (PI. XI. fig. 4.) 



The pterylosis of the embryo presents us with two distinct 

 phases. Stage 1 was kindly contributed by Prof. Newton, 

 and roughly corresponds with a 5-6-day chick embryo. 

 Here we have almost the earliest trace of feathers, which 

 appear as small papillse, mapping out the pterylse as seen in 

 the adult. The lower portion of the spinal and femoral 

 tracts are somewhat imperfectly preserved ; hence I cannot 

 be so certain as I could wish as to their precise form, but 

 I believe I have interpreted these parts correctly. 



* I propose to substitute the word filum in future in place of " cilium ;" 

 the special sense in which this latter word is now employed renders its use 

 in connection with feathers objectionable. I cannot \&,j claim, however, 

 to the credit of this renaming ; for, having brooded long and ineftectually 

 upon the point, I at last consulted Dr. Benham ( Aldrichian Demonstrator 

 of Comparative Anatomy), and he helped me out of my difficulty by 

 suggesting the highly appropriate term "filum." 



