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Sifting Bills
Frequently the edges of the mandibles and of the maxillae
are serrated to secure a firmer hold upon the food, for instance in Toucans.
In the Anseres
these tooth-like serrations are arranged in the shape of numerous transverse
lamellae, and hence the name "Lamellirostres," which, especially in the
Shoveler, form an elaborate sifting apparatus.
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The bill of the Flamingos is likewise furnished
with such sifting lamellae; the two halves of the under jaw are considerably
enlarged, so that the comparatively narrow upper jaw closes upon a wide
cavity. In addition to this the whole bill is bent downwards, in some species
rather abruptly; these long-necked birds being thus enabled to sift the
soft mud of lagoons with their bill in an inverted position, the dorsal
surface of the bill being turned towards the bottom. Undoubtedly this most
peculiar bill is a secondarily acquired character, referable to the mode
of feeding, which again is connected with the long neck and legs. This
view is strengthened by the fact that very young Flamingos still have straight
and short bills, which very gradually and only comparatively late assume
the final shape. Fine sifting lamellae occur also in Prion (WHALEBIRD),
and as a dense brushlike mass on the inside of the premaxillary region
in Anastomus.
The jaws. of this genus have the further peculiarity
that they do not shut completely, being, slightly curved in opposite directions.
Spatula and Spoonbills
In the Spoonbilled Sandpiper, Eurinorhynchus pygmaeus,
the end of the upper and lower bill is of a peculiar spatulate and
heart shaped form.
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The broad and flattened spatulate bill of the SPOONBILLS,
the boat or shoe-shaped bill of the Whale-headed STORK, Balaeniceps,
and of the Boatbill (Cancroma ), the long bills of the Ibis and
the Whimbrel, curved downwards, and upwards in the Avocet,
are all illustrations of the adaptation
to a special mode of life, and therefore not necessarily indicative of
relationship, as rather analogous than homologous structures.
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