Shape
Most bird eggs have an oval shape, with one end rounded and the other more pointed. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointy end develops at the back side. Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs.
The shape has biological significance. A pointed egg will tend to sit on its side, with the big end tipped upward. The big end contains the air sac and its shell is pierced by a higher density of pores than the more pointed end. Tipping the big end upwards improves oxygen flow to the large head, with the physiologically demanding eyes and brain, that develops in the big end while the tail develops at the more pointed end.
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Classic oval bird egg (Vanellus spinosus)
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Almost spherical bird egg (Senegal Parrot)
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Long, "elliptical" bird egg (Loon)
Read more about this topic: Bird Egg
Famous quotes containing the word shape:
“Is it true or false that Belfast is north of London? That the galaxy is the shape of a fried egg? That Beethoven was a drunkard? That Wellington won the battle of Waterloo? There are various degrees and dimensions of success in making statements: the statements fit the facts always more or less loosely, in different ways on different occasions for different intents and purposes.”
—J.L. (John Langshaw)
“Thir dread commander: he above the rest
In shape and gesture proudly eminent
Stood like a Towr; his form had yet not lost
All her Original brightness, nor appear’d
Less than Arch Angel ruind, and th’ excess
Of Glory obscur’d: As when the Sun new ris’n
Looks through the Horizontal misty Air
Shorn of his Beams, or from behind the Moon
In dim Eclips disastrous twilight sheds
On half the Nations, and with fear of change
Perplexes Monarchs.”
—John Milton (1608–1674)
“The work of the world is common as mud.
Botched, it smears the hands, crumbles to dust.
But the thing worth doing well done
has a shape that satisfies, clean and evident.
...
The pitcher cries for water to carry
and a person for work that is real.”
—Marge Piercy (b. 1936)