FRONT VIEW (A) AND SECTION (B) OF INFERIOR LARYNX OF PEREGRINE FALCON.(After Macgillivray.)
FRONT VIEW (A) AND SECTION (B) OF INFERIOR LARYNX OF PEREGRINE FALCON.(After Macgillivray.)
The ducts from the urinary organs open to the exterior through the cloaca, into which, as already mentioned, the digestive tube also opens. The chief point with regard to the urinary secretion of birds is the fact that it issemi-solid, and that it contains a quantity of the substance known asuric acid. The kidneys are placed some way back and near the cloaca; they are set on either side of the spinal column, between the transverse processes of the sacral vertebræ, and are generally divided into three portions of greatly varying size. On their inner edge are given off theureters, which pass on each side to enter separately into the before-mentioned cloaca.
The right ovary of birds is always atrophied, and it is in rare cases only that rudiments of it are found (namely, in the diurnal Raptores). Theoviductis a coiled canal, the lower portion of which has strong, muscular walls, while internally the characters of its surface vary according to the substance which the glands of different regions add to the descending egg. The right oviduct is not so completely atrophied as is the ovary of the same side. This duct opens into the cloaca through which the egg passes to reach the outer world; as further development is so largely independent of the mother, the female organs offer no peculiarities of arrangement, or complexities of structure.
All birds lay eggs, or, in other words, the born young are not carried about by the mother till the time of birth. The advantage of this to a flying animal is so obvious that we may pass at once to describe the egg of a common fowl. The shell, which consists of organic matter and lime-salts, is found to be formed of two layers; it is in the outer one only that pigment is found. Both layers are traversed by canals, through which air can pass only when the shell is dry;that is to say, the outer pores of the shell are closed under the influence of moisture. This may be seen by removing the outer layers, when air or water will pass in quite easily. These canals are said to be branched in the Ratite birds, and to be simple in the Carinatæ. The shell is lined by the shell-membrane, which, again, is made up of two layers. At the broad end of the egg these two layers are separated from one another, and so give rise to that air-chamber which is found in stale eggs, and increases in size as the egg grows older and the yolk evaporates.
The shell-membrane is in direct contact with thewhiteof the egg (albumen). This, in its fresh state, consists of fluid albumen, arranged in layers, which are separated from one another by networks of fibres, in the meshes of which, however, fluid albumen is also to be found. There are, further, two special sets of fibrous cords in the white of the egg; these extend somewhat along the long axis of the egg, though they do not reach to the shell-membrane. From their bead-like character they are known aschalazæ(hailstones), but their more common English name is that of the “tread.”
DIAGRAMMATIC SECTION OF A FOWL’S EGG.(bl) Blastoderm; (wy) White Yolk; (yy) Yellow Yolk; (vt) Vitelline Membrane; (w) Albumen; (ch) Chalazæ; (ach) Air-chamber; (ism) Internal Layer of Shell Membrane; (em) External Layer of ditto; (s) Shell.
DIAGRAMMATIC SECTION OF A FOWL’S EGG.
(bl) Blastoderm; (wy) White Yolk; (yy) Yellow Yolk; (vt) Vitelline Membrane; (w) Albumen; (ch) Chalazæ; (ach) Air-chamber; (ism) Internal Layer of Shell Membrane; (em) External Layer of ditto; (s) Shell.
The “white” is separated from theyolkby the so-calledvitelline(oryolk) membrane; the greater part of this yolk is known as theyellow yolk, and is made up of minute albuminous granules, but its outermost part is formed of a thin layer of a somewhat different substance, which goes by the name of thewhite yolk. The spheres of this latter are still smaller than those of the yellow yolk, and they are also found to form layers at various levels in it. At one point the white yolk becomes a good deal thicker, and forms, as it were, a pad for a small white disc, which, in ordinary circumstances, is always found uppermost when an egg is opened. This disc is formed of an encircling white rim, and within it there is a rounded transparent region, the centre of which is more opaque.
This region is known as theblastoderm, and is that part of the egg from which the chick, with its organs and complicated vessels, muscles and bones is soon to be developed. In the laid egg, this blastoderm consists of two layers of cells, as do at a certain stage the eggs of all but the very simplest of animals. The dissection of a laying fowl will probably reveal the presence of eggs at an earlier stage, and from their study the following history has been made out: the ellipse-shaped egg, when about to leave the ovary, is a yellow body enclosed in a fine membrane, and possessing at one pole a small (germinal) disc; this disc contains a smallergerminal vesicle, and a still smallergerminal spot; when this body is ripe, it escapes from its enclosing capsule, and the germinal vesicle disappears. As the egg passes down theoviductthe albumen becomes deposited around it, and part of it is converted into the shell-membrane. The egg now becomes subjected to a thick, white fluid, which is gradually converted into the shell.
While these additions to the substance of the egg are going on, the germinal disc undergoes the remarkable process known as segmentation, in which it becomes divided into two, four, eight, sixteen, thirty-two (and so on) masses, which arrange themselves in two distinct layers, the presence of which has been already noted in the laid egg.
This is not the place in which it is possible to follow out the various future changes undergone, but the condition of the young birds on escaping from the egg is widely different in some of the larger groups of birds. Some young birds, on their exclusion from the egg, are able to shift for themselves, and are covered with down; while others are born naked and helpless, and require food from their parents for some time after they are hatched. Of the first section, an ordinary chicken is a familiar example, while a young Thrush or a Sparrow illustrates the second. There are, however, manifest exceptions to this rule, as in the Herons, for instance, where the young are densely clothed with feathery down, but are helpless for a long time after they are hatched.
Finally, it must be stated that all birds possess an oil-gland (known as the uropygial), situatednear the tail, with which they clean and dress their feathers. Attention has already been called to this gland in the foot note on p. 245.
Before commencing the special part of the present article, it may be useful to give a slight sketch of the classification which it is proposed to follow throughout its course.
CLASS AVES.
DIVISION I. CARINATÆ: CARINATE BIRDS.
ORDER I.—ACCIPITRES: BIRDS OF PREY.
SUB-ORDERI.—FALCONES: FALCONS.
Family I.—Vulturidæ
Vultures.
„ II.—Falconidæ
Hawks.
Sub-Family I.—Polyborinæ
Caracaras.
„ II.—Accipitrinæ
Long-legged Hawks.
„ III.—Buteoninæ
Buzzards.
„ IV.—Aquilinæ
Eagles.
„ V.—Falconinæ
Falcons.
SUB-ORDERII.—PANDIONES: OSPREYS.
SUB-ORDERIII.—STRIGES: OWLS.
Family I.—Bubonidæ
Owls proper.
„ II.—Strigidæ
Barn Owls.
ORDER II.—PICARIÆ: PICARIAN BIRDS.
SUB-ORDERI.—ZYGODACTYLÆ: CLIMBINGBIRDS.
Family I.—Psittaci
Parrots.
a.Psittaci proprii.
Sub-Family I.—Camptolophinæ
Cockatoos.
„ II.—Androglossinæ
Fleshy-tongued Parrots.
„ III.—Conurinæ
Conures.
„ IV.—Platycercinæ
Parrakeets.
„ V.—Strigopinæ
Owl Parrots.
b.Psittaci orthognathi.
„ VI.—Trichoglossinæ
Brush-tongued Parrots.
Family II.—Cuculidæ
Cuckoos.
„ III.—Indicatoridæ
Honey-guides.
„ IV.—Musophagidæ
Touracoes.
„ V.—Picidæ
Woodpeckers.
„ VI.—Rhamphastidæ
Toucans.
„ VII.—Capitonidæ
Barbets.
SUB-ORDERII.—FISSIROSTRES: WIDE-GAPINGBIRDS.
Family I.—Galbulidæ
Jacamars.
„ II.—Bucconidæ
Puff Birds.
„ III.—Alcedinidæ
Kingfishers.
„ IV.—Bucerotidæ
Hornbills.
„ V.—Upupidæ
Hoopoes.
„ VI.—Meropidæ
Bee-eaters.
„ VII.—Momotidæ
Motmots.
„ VIII.—Coraciadæ
Rollers.
„ IX.—Trogonidæ
Trogons.
„ X.—Caprimulgidæ
Goatsuckers.
„ XI.—Cypselidæ
Swifts.
„ XII.—Trochilidæ
Humming-birds.
ORDER III.—PASSERIFORMES: PERCHING BIRDS.
SECTIONA.—ACROMYODI: SINGINGBIRDS.
SUB-ORDERI.—TURDIFORMES: THRUSH-LIKE. BIRDS.
GROUPI.—COLIOMORPHÆ: CROW-LIKE. PASSERES.
Family I.—Corvidæ
Crows.
Sub-Family I.—Corvinæ
Crows proper.
„ II.—Fregilinæ
Choughs.
„ II.—Paradisiidæ
Birds of Paradise.
„ III.—Orioliidæ
Orioles.
„ IV.—Dicruridæ
Drongos.
„ V.—Prionopidæ
Wood-shrikes.
GROUPII.—CICHLOMORPHÆ: THRUSH-LIKEPASSERES.
Family VI.—Campophagidæ
Cuckoo-shrikes.
„ VII.—Muscicapidæ
Flycatchers.
„ VIII.—Turdidæ
True Thrushes.
Sub-Family I.—Turdinæ
Thrushes.
„ II.—Sylviinæ
Warblers.
Family IX.—Timeliidæ
Babbling Thrushes.
Sub-Family I.—Troglodytinæ
Wrens.
„ II.—Brachypodinæ
Bulbuls.
„ III.—Timeliinæ
Babblers.
„ IV.—Cisticolinæ
Grass-warblers.
„ V.—Miminæ
American Babblers.
Family X.—Laniidæ
Butcher-birds.
„ XI.—Vireonidæ
Greenlets.
„ XII.—Paridæ
Titmice.
GROUPIII.—CERTHIIMORPHÆ: CREEPERS.
GROUPIV.—CINNYRIMORPHÆ: HONEYSUCKERS.
SUB-ORDERII.—FRINGILLIFORMES: FINCH-LIKEBIRDS.
Family I.—Motacillidæ
Wagtails.
„ II.—Mniotiltidæ
American Warblers.
„ III.—Cærebidæ
American Creepers.
„ IV.—Diceidæ
Flower-peckers.
„ V.—Ampelidæ
Chatterers.
„ VI.—Hirundinidæ
Swallows.
„ VII.—Tanagridæ
Tanagers.
„ VIII.—Fringillidæ
Finches.
„ IX.—Icteridæ
Hang-nests.
SUB-ORDERIII.—STURNIFORMES: STARLING-LIKEBIRDS.
Family I.—Ploceidæ
Weavers.
„ II.—Sturnidæ
Starlings.
„ III.—Artamidæ
Wood-swallows.
„ IV.—Alaudidæ
Larks.
SECTIONB.—MESOMYODI: SONGLESSBIRDS.
Family I.—Menuridæ
Lyre-birds.
„ II.—Pteroptochidæ
Bush-wrens.
„ III.—Dendrocolaptidæ
Spine-tails.
„ IV.—Formicariidæ
American Ant-thrushes.
„ V.—Pittidæ
Old-World Ant-thrushes.
„ VI.—Tyrannidæ
Tyrant-birds.
„ VII.—Cotingidæ
American Chatterers.
„ VIII.—Pipridæ
Manakins.
„ IX.—Eurylæmiidæ
Broadbills.
„ X.—Phytotomidæ
Plant-cutters.
ORDER IV.—COLUMBÆ: PIGEONS.
ORDER V.—GALLINÆ: GAME-BIRDS.
Family I.—Cracidæ
Curassows.
„ II.—Opisthocomidæ
Hoatzins.
„ III.—Phasianidæ
Pheasants.
„ IV.—Meleagridæ
Turkeys.
„ V.—Tetraonidæ
Grouse.
„ VI.—Pteroclidæ
Sand-grouse.
„ VII.—Turnicidæ
Hemipodes.
„ VIII.—Megapodidæ
Megapodes.
ORDER VI.—GRALLÆ: WADING BIRDS.
Family I.—Rallidæ
Rails.
„ II.—Scolopacidæ
Snipes.
„ III.—Charadriidæ
Plovers.
„ IV.—Otididæ
Bustards.
„ V.—Gruidæ
Cranes.
„ VI.—Psophiidæ
Trumpeters.
ORDER VII.—HERODIONES: HERONS.
Family I.—Ardeidæ
Herons proper.
„ II.—Ciconiidæ
Storks.
„ III.—Plataleidæ
Spoonbills.
„ IV.—Phænicopteridæ
Flamingoes.
ORDER VIII.—ANSERES: GEESE.
Family I.—Palamedeidæ
Screamers.
„ II.—Anatidæ
Ducks.
ORDER IX.—STEGANOPODES: PELICANS.
Family I.—Fregatidæ
Frigate-birds.
„ II.—Phæthontidæ
Tropic-birds.
„ III.—Pelecanidæ
Pelicans.
ORDER X.—GAVIÆ: SEA-BIRDS.
Family I.—Laridæ
Gulls.
„ II.—Procellariidæ
Petrels.
ORDER XI.—PYGOPODES: GREBES.
ORDER XII.—IMPENNES: PENGUINS.
ORDER XIII.—CRYPTURI: TINAMOUS.
DIVISION II.—RATITÆ: STRUTHIOUS BIRDS.
DIVISION III.—SAURURÆ: LIZARD-TAILED BIRDS.
It has been already stated that birds are divisible into three great sections, and attention is now directed to those which have a keel to the sternum, and which are good flyers—the Carinate Birds (CARINATÆ).