MadSci Network: Agricultural Sciences

Re: Is it true that the eggshell is formed after the egg is laid?

Date: Mon Oct 12 00:23:38 1998
Posted By: Wendy Ingman, Grad student, Obstetrics and Gynaecology Department, University of Adelaide
Area of science: Agricultural Sciences
ID: 903984270.Ag

Dear Ramiro,

The eggshell consists of two membranes, a mineralised shell (which is made 
up of almost pure calcium carbonate) and a proteinaceous cuticle. 
The membranes are the slightly leathery layers which you find 
underneath the hardened shell when you break open an egg. Calcification of 
the shell begins in the female's reproductive tract in the area called the 
isthmus. The egg then moves to the shell gland where it spends about 20 
hours, this is where most of the mineralised part of the shell is formed. 
The cuticle is also added here. When the egg is laid, it has every 
component of its shell however the shell is still reasonably soft. The 
shell hardens once it has been laid. Shell hardening is not related to 
This information can be found in "Reproduction of Farm Animals" (1974) by 

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