WING OF EMBRYO PENGUIN. 19 
appearance of the first bone cells ; so much so, that all the essential characters of the 
adult paddle are present, in the case of the Emperor Penguin, for example, long before 
the beak has acquired its typical shape, and while the feathers are as yet but papille 
(Pl. fig. 10). 
Let us compare the wing of an embryo Pygoscelis adelie on the one hand with 
that of an adult of the same species, and on the other with that of a somewhat later 
embryo of Aptenodytes forstert. In the wing of the younger embryo it will be noticed 
that ossification is just beginning to take place in the bones of the forearm, and that 
these are more or less dumb-bell shaped, and circular in section. The carpal elements 
are as yet distinct, the radiale being wedge-shaped, instead of cuboid, as in the adult, 
and the ulnare almost cuboid, instead of triangular, as in the adult; while the distal 
elements of the carpus are three in number. Carpale 1 is small, spherical, and not 
very sharply differentiated from the embryonic tissue, and this is also true of carpale 
3. Carpale 2 forms a large semilunar plate closely applied to the base of its meta- 
carpal. The metacarpalia are all distinct, Mc. I being short and placed at an angle with 
Me. II, which is long, cylindrical, and expanded at each end, while Me. III is rod-like 
and extends distad beyond Me. II. The phalanges are long, and also cylindrical. The 
terminal phalanx of Digit IT, it is to be noted, is constricted round its middle, and has its 
free end expanded in such a way as to suggest an earlier phylogenetic stage when this 
digit bore an ungual phalanx. The phalanx of Digit III is remarkable for its great length, 
and forms a slender cylindrical rod, slightly bowed, and extending as far as the middle 
of the terminal phalanx of Digit III. From the somewhat hastate shape of its free end 
we may infer that this digit was armed with a claw up to within comparatively recent 
times. Though as development proceeds this phalanx changes shape, and loses some- 
thing in length, it remains throughout life unique among birds for its great size. 
The figure of this wing of Pygoscelis (Pl. fig. 9), should now be compared with that 
of embryo Emperor Penguin (Aptenodytes forstert) (Pl. fig. 10). Though apparently 
the bird from which this wing was taken was but little older than that of the Pygoscelis 
adeliz just described, it has assumed all the principal features of the adult wing, and 
this fact will become the more obvious in comparison with Pl. figs. 10-11. In the 
preparation from which this drawing was made the primary cartilaginous skeleton can still 
be traced, though in places the absorption of the cartilage by the growing bone cells has 
begun. The rod-like form of the long bones has now become transformed into broad 
bars, the carpus has assumed its adult form, but the pollex is yet free. Though Digit 
II bears an ungual phalanx, this appears to be wanting in Digit II; possibly, however, 
a slightly later stage would show that the cartilage segments to form this, and that it 
remains distinct for some time. 
Between this wing and that of the adult there is less difference. The most striking 
feature indeed is the disappearance of the pollex, which can now only be traced with 
difficulty, since it has fused completely with the metacarpal of Digit II, leaving at most 
but a single groove or a few perforations along the line of fusion. Digit II. loses its 
Ba 
