MOULTING OF PENGUINS. 13 



main shaft. In other species, though a main shaft and hyporhachis are present, the 

 radii are much more degenerate. 



Some time since I drew attention to the fact (15) that though in the Casso- 

 wary and Emu the definitive feather bore an after shaft as long as the main shaft, 

 in the nestling down the after shaft was barely traceable ; while on the other hand the 

 definitive feather of the Tinami possessed but a small or vestigial after shaft, while the 

 " nestling down " had a hyporhachis as large as its main axis, thus reversing the order 

 between adult and young in the two groups. It now appears probable that what have 

 hitherto been regarded as the definitive feathers of the Cassowary and Emu are really 

 to be looked upon as answering to the " mesoptyles " of the Tinami. That is to say, 

 these birds, though they may have developed remiges of the normal definitive type, yet 

 never acquired the feathers of this grade on the trunk. A parallel condition is seen 

 among living birds to-day in the owls. The young Tawny Owl for many weeks is 

 clothed, as to his trunk, in mesoptyles, but the remiges, which are functional, are those 

 of the higher type of feathers. Apteryx certainly must be regarded as having lost the 

 true nestling down ; what is generally regarded as nestling down, and has been 

 described as such by myself (15), represents a mesoptyle plumage. The nature of the 

 nestling plumage of the remaining Struthious types will now require further study. 

 To show how complex is this problem of nestling plumage it may be pointed out that 

 in some birds, as, for example, Plialacrocorax, the first plumage is made up entirely of 

 pre-plumula3, while in other Steganopodes it is composed of pre-pennse. In some of this 

 group it may turn out that the plumage is composed of a mixture of both. The fact 

 that in the penguins the rami of each mesoptyle are connected by means of a long 

 ribbon-shaped stalk with the aftershaft of the definitive feather is one which must form 

 the subject of further examination. At present no solution appears possible. 



IV. THE MOULTING OF THE ADULT PENGUIN. 



THE penguins appear to be peculiar in the method of their moulting, inasmuch as 

 the feathers are not cast a few at a time, but over large areas the feathers of the 

 moulting bird will be found to have actually lost all direct attachment to the body, 

 and to stand out therefrom at right angles or thereabouts. 



The moulting of the feathers has been described by more than one observer, but 

 with especial care by the late Mr. A. D. Bartlett (2), and more recently by Mr. W. E. 

 De Win ton (5). The former, just seven and twenty years ago, gave a short account 

 of the moulting of Humboldt's Penguin (Spheniscus humboldtf). The feathers of the 

 wing, he wrote, " came off like the skin of a serpent." But the feathers, he says, in 

 speaking of the moulting of the trunk, " began to fall from all parts of the bird, not as 

 birds usually moult, a few feathers at a time, but in large quantities." These old 

 feathers were pushed off, he says, by the new ones, many of the old feathers being left 



