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:
“In almost all climes the tortoise and the frog are among the precursors and heralds of this season, and birds fly with song and glancing plumage, and plants spring and bloom, and winds blow, to correct this slight oscillation of the poles and preserve the equilibrium of nature.”
—Henry David Thoreau (1817–1862)
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