Question: how to chickens make egg shells

Shikha Sharma answered on 11 Nov 2014:

Hi Clodagh,
That’s an interesting question. Eggs are perfect example of amazing display of nature’s process. In chickens, the process of making the hard shell takes about 20 hours that is why a hen lays only 1 egg/day. In birds, the developing egg first enters into a part of the reproductive tract (isthmus) that secretes two soft membranes that surround the egg. If you boil an egg, you can sometimes peel away the membrane. Then from there the egg moves into another area called the “shell gland.” The cells of this gland secrete the shell material, which covers the egg. In birds, the shell usually hardens (“calcifies”). After the shell material coats the egg, the egg passes through the rest of the reproductive tract and is “laid.” 🙂