Re: How do chickens lay eggs without breaking them?

Well the simple answer is because that is how their bodies work.  I think you
might want the more complex answer so here goes...

The process of egg  production falls under the hen's hormonal control from
gonadotrophins that are produced by the anterior pituitary gland.  And
ovulation-inducing hormone is released by the pituitary and if there is enough
mature follicle available it will ovulate in about 4-8 hours.  The vitelline
membrane is the transparent casing that encloses the yolk of the hens egg and 
separates it from the albumen.  This then is made up of two layers, the inner
layer, which is laid down in the ovary and the outer layer which is secreted in
the oviduct.  It is made up of a fiber which are rich in glycoproteins. 
The inner layer is about 1-3.5 microns thick and consists of a meshwork of solid
cylindrical fibres that run parallel to the surface of the yolk, these vary in
thickness.  The outer layer is about .3-.9 microns thick and is composed of a
variable number of sublayers.  It also contains fibers but these are thinner
than those of the outer.  Basically they are an encasing shell of protein.

About 91% of the shell consists of inorganic matter/ and about 98% of that is
calcite, the remaining 2%is magnesium carbonate and tricalcium phospate.  The
calcite crystals are arranged in columns which extend almost through the entire
thickness of the shell and are really closely packed together.  Gaps between
them act as pores. It is also covered by a thin cuticle, no one has of yet
figured out why as it is only present in chicken eggs and no other birds.  The
egg travels from the upper levels of the reproductive tract into the lower
levels where the formation of the primitive streak begins to show.

So basically the yolk type substance is deep inside the chicken, as it passes
throught the reproductive organs it gets layers upon layers of a harder surface
to encapsulate it.  These are made up of a substance that acts as a barrier
against any foriegn objects yet allows moisture and oxygen to pass.  The chicken
has muscles that allow the egg to slowly slide down into the lower levels until
it passes fully formed (hopefully) out the other end.

Hope this helps