20 EDWARD A. WILSON. 
in a sheet or “slough,” and suggesting a comparison with the sloughing of a reptile’s 
skin. The comparison, however, as Mr. Pycraft has elsewhere shown, is fallacious, and 
as misleading in its suggestion as the use of the word ‘‘ pouch” in describing the same 
bird’s incubation methods. 
In all probability, not only are the superficial scales of the feet shed as well as 
the feathers, but also the plate on either side of the lower mandible, as in the case of 
the Puffin and possibly the Auk* and other birds. The superficial layers of these 
horny parts, at any rate, become loose, and, in the Emperor, change the colour of the 
beak, rendering it dull and opaque, and the feet brown instead of black. The coloured 
plates of the lower mandible can easily be removed in a moulting bird, and are 
then found to be of a translucent yellow horn. 
In the young chick the colouring of the iris is a rich dark brown, varying a trifle in 
warmth from dark walnut, though never reaching the redness of mahogany. The bill 
is blackish at the tip and base and whitish in the centre, while in the older chicks there 
is sometimes a faint dusky purplish tinge in the lower bill. The feet and nails, at 
first pale fleshy grey or the colour of French chalk, become darker day by day, till in 
the third week they are definitely black. 
In the immature bird, after shedding the downy feathers, the whole of the back 
becomes bluish grey, the blue tinge preponderating and encroaching on the head and 
neck. The chin is grey and mottled, but the throat, instead of being black as in the 
adult, is white, with here and there a greyish feather showing through, though in some 
the demarcation line between the dark chin and the white throat is quite distinct, as 
in Fig. 3 of Birds, Plate III. If this figure be examined and compared, first with the 
arrangement of black-and-white in the chick, Figs. 1 and 2, Plate III, and then with 
the head represented in Fig. 4, it will be seen to show a kind of transition stage in 
which the white round the orbit in the chick has not quite changed to the dark grey 
characterising Fig. 4, Plate II]. Neither has the grey patch on the side of the neck, 
the precursor of the orange in the adult, come out so prominently in Fig. 3, Plate III., 
as it has in Fig. 4, Plate III. This is due to a variable admixture of grey feathers with 
the white and white with the grey, as the case may be. The iris in this stage also is 
a rich dark brown, and the bill has become dusky throughout, with a dull purple tinge 
upon the lower mandible. The feet are black, as also are the claws; this holds good 
for the adult bird as well. The beak, however, alters, and in Figs. 5 and 6, Plate IIL, 
it will be seen that the side plates of the lower bill now show a decided orange 
yellow tint, less marked than in the fully adult bird, but still distinct. These two 
heads are drawn from birds in the same plumage as Nos. 3 and 4, Plate III, but after a 
full year’s weathering, which has faded the black to brown and has much reduced the 
prominence of the blue or bluish grey. The whole plumage in this stage has a brown 
and faded appearance, and the patch on the side of the neck has become quite white. 
In No. 6, Plate IE., the demarcation of the black throat of the adult is already 
* Puffin = Fratercula arctica; Auk = Mergulus alle. 
