36 BILL—BIRD 
position, but the right nostril, and still more the groove, are 
perceptibly slanting towards the right, as can be ascertained by 
viewing the bill from the dorsal side. 
Sexual DrMoRPHISM is mostly restricted to peculiarly shaped 
bills ; for instance, the horn of the male Hornbills is often larger, 
and differs in shape from that of the female. In the males of 
Pelicans several unpaired excrescences are formed entirely by the 
horny coating of the premaxilla ; they sometimes reach a height of 
three to four inches, and are again cast off after the breeding 
season, resembling in the latter feature the Auks, as described 
above. : 
The most striking example of dimorphic bills is that of the New- 
Zealand Huta, Heterolocha, the bill of the female being slender, 
about four inches long, and much curved, while that of the male is 
nearly straight, stout, and scarcely half that length. The knobs or 
swellings in the Galline are mostly restricted to the males; the 
same applies to Gidemia (Scorer). Sexual differences in colour 
are common. For instance, in the male Scoter the bill is black and 
orange, in the young and in the female it is simply grey, and with- 
out the knob. The bill of the adult male BLACKBIRD is orange- 
yellow ; that of the young of both sexes and of the adult males of 
Buceros malayanus (HORNBILL) is white, but becomes black in the 
adult female, forming thus an interesting exception to the general 
rule that the young agree with the females, and that aberrant 
coloration is confined to the males. The colour of the bill is 
deposited as a diffused pigment in the horny cells of the epidermal 
coat, but is occasionally restricted to the deeper layers, or even 
to the Malpighian layer itself, then shining through the outer 
transparent layers. . 
In connexion with the bill is to be mentioned the “egg-tooth,” 
which is developed in the embryos of all birds as a small whitish 
protuberance or conglomeration of salts of calcareous matter, 
deposited in the middle layers of the epidermis of the tip of the 
upper bill, without being connected with the premaxilla itself. 
The sharp point of this “tooth” soon perforates the upper layers 
of the horny sheath, and then files through the eggshell, a slight 
crack in the latter being sufficient to enable the young bird to 
free itself. A similar egg-tooth exists in Reptiles, and is, as in 
Birds, cast off after hatching. The wearing away of the growing and 
constantly renewed horny layers of the bill can be easily observed 
in the pealing beak of a Parrot. 
BIRD (etymology unknown; but in Old English brid), origin- 
ally the general name for the young of animals;! then, as the 
1 Asin Wyclif’s translation of Matth. xxiii. 33, ‘‘eddris, and eddris briddis ” 
(A.V. ‘‘serpents” and “‘ generation of vipers’); Trevisa, Barth de P. R. xii. v. 
