THE EMPEROR PENGUIN. 21 
definitely marked by the appearance of a few black feathers. On this plate then are 
represented the heads of three distinct phases of plumage, Nos. 1 and 2 giving the 
heads of chicks in down in the first 4 months, Nos. 3 and 4 giving the heads of 
immature birds at 5 months and onwards; this gradually weathering to the condition 
of the heads figured in Nos. 5 and 6, which are drawn from birds of 18 months, when 
they are on the point of moulting for the first time into the black-throated, yellow- 
necked dress of the adult. 
The first adult livery is, as I have said, not quite so rich in colour as it becomes 
after another moult, but is in other respects similar, and so has not been figured. 
Plate II. represents the life-size head of an adult Emperor in full plumage, with 
the rose and lilac colour fully developed on the lower bill, and the head and throat a 
rich glossy black against the bright orange yellow on the neck. Had the weathered 
and faded condition of the adult livery been represented, it would have shown again 
how much of the black fades out to a dull brown colour, both on the head and neck 
and hack, the blue hardly changing, but giving with the brown a very faded 
appearance to the plumage. The tail feathers, twenty in number, become worn to 
mere quills, and often in the breeding rookery one may find all the tail feathers 
detached from the bird and lying imbedded in a large lump of hard and dirty ice: upon 
the floe. The scales on the feet also will be no longer a rich black, but brown. 
If one compares the measurements of the birds in these various stages of 
growth, one finds that great changes are effected in the bill. It will be seen 
by comparing Figs. 3 and 4 with Figs. 5 and 6 of Plate III., that the chief 
alteration takes place by the lengthening of the upper mandible, the curve of 
which gradually increases. With this growth proceeding at a faster rate along the 
culmen than along the tomia, the nostrils, which are very definite and well marked 
in the first few months of life, gradually become obscured. So also the thickening, 
which is apparent on the culmen about one-fourth of its length from the tip, is also 
gradually obliterated by the elongation of the upper mandible. This thickening has 
served in place of an egg scale, which is not developed as a deciduous element at all. 
The angle of the gonys, too, which is quite apparent in the lower mandible up to the 
fifth month, gradually disappears with the lengthening of the bill, and eventually the 
strong uniform curve of the adult bill developes to its full extent. 
Perhaps the measurements which best bring out these changes in the growth 
of the bill are the length of the upper mandible from the feathers at the nostril to the 
tip, and the measurement from the angle of the mouth to the tip of the bill. Thus:— 
Nostril to Tip. Gape to Tip. 
At 5 months Sieg kg . 85 em. iG Le, .. Sl em. 
At 18 months sa vo .. 4°3 cm. ae wa .. 93 cm. 
At 20 months... tee .. (broken)... oy . 10°5 em. 
At 30 months and onwards .. 4°53 cm. as sak .. 11°8 cm. 
The adult measurements of the wings are reached much earlier, even within the 
first six months, as also are the measurements of the feet and claws, presumably as a 
