WING OP 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 papillae 

 (PL fig. 10). 



Let us compare the wing of an embryo Pygoscelis adelise 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 forsteri. 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, Me. I being short and placed at an angle with 

 Me. II, which is long, cylindrical, and expanded at each end, while Me. Ill is rod-like 

 and extends distad beyond Me. II. The phalanges are long, and also cylindrical. The 

 terminal phalanx of Digit II, 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 (PI. fig. 9), should now be compared with that 

 of embryo Emperor Penguin (Aptenodytes forsteri) (PI. fig. 10). Though apparently 

 the bird from which this wing was taken was but little older than that of the Pygoscelis 

 adelise just described, it has assumed all the principal features of the adult wing, and 

 this fact will become the more obvious in comparison with PI. 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 III ; 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 



P 2 



