Birds
In birds, the process of breaking open the eggshell is commonly referred to as pipping.
Chicks have a pipping muscle on the back of their necks. It is this muscle which gives them the strength to force the egg tooth through the inner membrane of the eggshell.
When a chick becomes too large to absorb oxygen through the pores of its eggshell, it uses its egg tooth to peck a hole in the air sac located at the flat end of the egg. This sac provides a few hours worth of air, during which the chick breaks through the eggshell to the outside. The egg tooth falls off several days after hatching.
Kiwis lack an egg tooth, instead using their legs and beak to break through a relatively thin eggshell. The superprecocial megapodes possess an egg tooth in their early embryonic development, but instead use their claws during hatching.
Read more about this topic: Egg Tooth
Famous quotes containing the word birds:
“poems direct as what the birds said,
hard as a floor, sound as a bench,
mysterious as the silence when the tailor
would pause with his needle in the air.”
—Denise Levertov (b. 1923)
“These beginnings of commerce on a lake in the wilderness are very interesting,—these larger white birds that come to keep company with the gulls.”
—Henry David Thoreau (1817–1862)
“We cannot do without it, and yet we disgrace and vilify the same. It may be compared to a cage, the birds without despair to get in, and those within despair to get out.”
—Michel de Montaigne (1533–1592)