THE EMPEROR PENGUIN. 25 



to simulate a shadow. But as has already been shown, it probably has no urgent need 

 for being inconspicuous. 



We are therefore led to consider whether the black head, which at rest may be an 

 additional help to inconspicuousness, might not be a boon when in motion to the 

 parent, assisting it to find its young after a prolonged stay under water, during which 

 the movements of the ice may have altered all its bearings. 'This might be considered 

 a partial explanation, but can hardly be the whole of the matter, for the shrill and 

 piping voice of the chick is a very serviceable equipment against such an eventuality 

 as separation from its parent, and again, if a black head is helpful as a beacon, much 

 more so would be a uniformly dark head and body, as in the chicken of the King. 



I must confess therefore to an inability to explain the facts of the case in the 

 colouring of this chick, and I am forced to turn for an explanation away from the 

 overburdened theories of protective assimilation, and even of advantageous colouration 

 at all from any but a physiological standpoint. In this particular case, even 

 physiologically, it is hard to see why the Emperor's chick should not have dispensed 

 with the pigmentation of its head, and have done all that was possible to economise 

 its energies by becoming wholly white. 



I cannot think that in the adult stage the Emperor Penguin was ever white. The 

 white down of the chick must be a special development of its own, probably upon the 

 lines of physiological economy. Such pigment as it was able to produce instead of being 

 squandered over the whole body, as it is in the young King Penguin, is in the young 

 Emperor concentrated in the head as black, where it may be of use as a signpost to its 

 parent in the pack ice in the manner above suggested. This may on the whole cost 

 each individual less than it would to pigment the whole of the down, and in the 

 September temperatures of the Antarctic even the most trifling effort at physiological 

 economy may turn the scale. 



I know that in thus trying to suggest an explanation for this particular case I am 

 falling back on what is still an uncertain theory, but in what has been published 

 concerning the physiological reasons for colour or its absence in various animals, there 

 is sufficient truth to encourage the suggestion of further examples which appear to 

 uphold the theory. In the case of white animals, moreover, whose whiteness is 

 generally due to the absence of pigment in hair or feather, one is on safer ground, for 

 there is no doubt' that the production of much pigment is associated with an active tissue 

 metabolism, and that the production of little pigment is associated with a metabolism 

 in which economy is obviously of importance, e.g. , old age and winter whitening. 



It is possible, moreover, though I know of no experiments that have been made 

 upon the subject, that white feathers and white hair, in which the cellular tissue is 

 occupied by air instead of solid pigment may prove to be a more satisfactory non- 

 conducting material than pigmented hair or feathers. If this is so, we have a definite 

 physiological reason for the whiteness which characterises so many of the Polar animals, 

 and indeed for the whiteness of certain Tropical species, for the conditions which would 



