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. Apteryzx 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, Phalacrocoraz, the first plumage is made up entirely of 
pre-plumulz, while in other Steganopodes it is composed of pre-pennz. 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.—Taxr Movttine or 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 Winton (5). The former, just seven and twenty years ago, gave a short account 
of the moulting of Humboldt’s Penguin (Spheniscus humboldti). 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 
