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:
“To warm their little Loves the Birds complain:”
—Thomas Gray (1716–1771)
“Novelists do not write as birds sing, by the push of nature. It is part of the job that there should be much routine and some daily stuff on the level of carpentry.”
—William Golding (b. 1911)
“Because humans are not alone in exhibiting such behavior—bees stockpile royal jelly, birds feather their nests, mice shred paper—it’s possible that a pregnant woman who scrubs her house from floor to ceiling [just before her baby is born] is responding to a biological imperative . . . . Of course there are those who believe that . . . the burst of energy that propels a pregnant woman to clean her house is a perfectly natural response to their mother’s impending visit.”
—Mary Arrigo (20th century)