NESTLING DOWN OF PENGUINS. 11 
tions of the penguins herein described. The nestlings of these birds, as has already 
been pointed out (p. 6), before attaining the typical contour feathers, develop two 
distinct down plumages. Inasmuch as these neossoptiles are commonly split up by the 
succeeding contour feather, so that each of the terminal rami of the latter is surmounted 
by a ramus of the disintegrated down feather, it has been suggested that these down 
feathers are really a part of the actual contour feather. 
Though Studer (20), Davies (4), Klee (9), and others have contributed some valuable 
observations on the development of nestling down and contour feathers, there is much 
work yet to be done on the embryonic history of the feather—much that as yet remains 
obscure, but is essential to a thorough grasp of this question. But there can be no 
doubt that the neossoptyles represent distinct feather generations. That later they 
become, in so many instances, disintegrated, so that the several rami of which they are 
composed are borne out on the tips of the rami of the succeeding definitive feather, is 
due to the fact that the growth of the definitive feather is begun before that of the 
neossoptile has finished, and consequently the bases of the rami of the first become 
welded on to the tips of those of the second, as will be made apparent presently. Let 
this be assumed as proved for the moment, and it will be seen that a new and important 
light is thrown not only on the sequences of the plumages of the penguins in particular, 
but of the nestling and later plumages of all birds. The penguins then develop two 
successive down plumages before assuming the normal definitive feathers. The point 
to be discovered is the significance of this sequence ; and this can best be done by a 
general and brief survey of what obtains in other groups. 
Up till the present it has never been suspected that more than one generation of 
nestling down was ever developed,* though it has long been known that the succeeding 
generation of definitive feathers, in some species, presents a character intermediate 
between down and the contour feathers which eventually succeed them. Further, as I 
have already pointed out on more than one occasion, these down feathers present very 
different grades of perfection, such for example as may be seen in the umbelliform tufts 
of loose, woolly down of, say, an owl, the semi-plumous type of the Galli and Anseres, 
and the strongly pennaceous type of some Tinami. It has now become necessary to 
re-interpret the significance of these differences. It would seem, then, that the full 
sequence of plumages is represented (1) by neossoptyles, composed of (A) pre-penne, 
divisible into a—protoptyles and B—mesoptyles; (B) pre-plumule, and (2) teleoptyles 
or definitive feathers. 
In how many groups of birds these three plumages are represented I am at present 
unable to say, but I have undertaken, in conjunction with my friend Mr. J. L. Bonhote, 
a thorough examination of this problem. Consequently, I propose to do little more 
* Since this was written, a paper has appeared (‘‘ Ibis,” Jan. 1906) from the pen of Mr. W. Eagle Clarke, on 
the results of the Scottish National Antarctic Expedition. He therein briefly refers, without special comment, to 
the fact that in the young of the Gentoo Penguin, Pygoscelis papua, the down of the newly-hatched chick ‘soon 
gives place to a darker coat of down, to the tips of which the paler down of the first coat is attached 
for a time.” 
