when does the hard calcium shell form around the egg
Eggshell The fibrous chicken shell membranes are added in the proximal (white) isthmus of the oviduct.[1] In the distal (red) isthmus mammillae or mammillary knobs are deposited on the surface of the outer membrane in a regular array pattern.[7][8] The mammillae are proteoglycan-rich and are thought to control calcification. In the shell gland (similar to a mammalian uterus), mineralization starts at the mammillae. The shell gland fluid contains very high levels of calcium and hydrogen carbonate. The thick calcified layer of the eggshell forms in columns from the mammillae structures, and is known as the palisade layer. Between these palisade columns are narrow pores that traverse the eggshell and allow gaseous exchange. The cuticle forms the final, outer layer of the eggshell.[9]
Fallopian tube The tube allows passage of the egg from the ovary to the uterus. When an oocyte is developing in an ovary, it is encapsulated in a spherical collection of cells known as an ovarian follicle. Just prior to ovulation the primary oocyte completes meiosis I to form the first polar body and a secondary oocyte which is arrested in metaphase of meiosis II. This secondary oocyte is then ovulated. The follicle and the ovary's wall rupture, allowing the secondary oocyte to escape. The secondary oocyte is caught by the fimbriated end and travels to the ampulla of the uterine tube where typically the sperm are met and fertilization occurs; meiosis II is promptly completed. The fertilized ovum, now a zygote, travels towards the uterus aided by activity of tubal cilia and activity of the tubal muscle. The early embryo requires critical development in the Fallopian tube.[2] After about five days the new embryo enters the uterine cavity and on about the sixth day implants on the wall of the uterus.