22 EDWARD A. WILSON. 



result of the necessity for extra strength and efficiency in those parts to avoid natural 

 enemies over and above their uses in obtaining food, while the bill lacks this stimulus 

 to rapid growth. 



The individual variation to be found in a series of Emperor Penguins 

 amounts to very little indeed. When the variation in size and weight has been 

 mentioned, as illustrated in the series of thirty-three birds given above, there is 

 no special point to which attention can be drawn except in the curve of the bill. Here, 

 however, there is some variation having no apparent reference to sex or age. In some 

 individuals the curve is decidedly more marked than in others, as may be seen, for 

 example, in the two birds of a similar age in Figs. 5 and 6 of Birds, Plate III. This is 

 not merely characteristic of immaturity, for the curved type shown in Fig. 5 is found 

 even more strongly marked in some of the adult specimens in the collection. 



The colour of the side plate of the lower mandible is also variable, from yellow 

 through orange and red to lilac ; but it seems to depend to a certain extent on the 

 condition of the peripheral circulation, turning to a livid lilac when the circulation 

 is depressed by cold. The depth of the lemon-yellow colour of the Itreast and 

 abdominal feathers varies considerably according to the extent to which the summer 

 sun has faded it. When freshly moulted the whole of the lower parts must be de- 

 scribed as pale lemon yellow, not white, as in the catalogue of the British Museum. 



In describing the immature bird also there is a point worth noting in the colour 

 of the crown, which is of pale bluish grey, marked oflT as a distinct patch from the 

 darker grey which surrounds it. This bluish patch is noticeable during the first 

 seventeen months, but the head then becomes jet l)lack all over. The point is the 

 more interesting because it is exactly reproduced in the first prenuptial plumage of the 

 immature King Penguin. As a grey coronal patch it is lost in both King and Emperor 

 when the immature plumage is discarded, but in the King the tendency to differentiate 

 in colour in this part of the head is again brought out by the deposition of minute 

 quantities of golden yellow pigment in the coronal and particularly the superciliary 

 feathers, which with the black gives the crown a greenish sheen. This is also to 

 be seen upon the chin and throat. That this tendency to deposit golden yellow 

 pigment should occur in the position in which the golden superciliary crests occur 

 in Catarrliactes and Megach/ptes is most significant, and an examination of a specimen 

 of the King Penguin in the collection of the British Museum, now figured for the 

 first time in Fig. 4 of Birds, Plate VIII., will show how far this tendency may be 

 carried in a particularly vigorous individual. 



Attention is particularly drawn to the distribution of the golden yellow pigment in 

 this specimen, because it has a definite bearing on the genesis of the superciliary crests 

 in those genera which normally possess them. To this end I have gone into some 

 detail in describing the head and neck of this particular specimen in the chapter devoted 

 to Aptenodytes jMtagonica {-pp. 35, 36), and there the question of its relationship to 

 Aptenodytes forsteri is dealt with more fully. 



