At approximately day 1

Mammary vasculature is well formed.

Reference [PubMed Link]

Laurence DJ, Monaghan P, Gusterson, BA. 1991. The development of the normal human breast. Oxford Reviews of Reproductive Biology 13:149-174.

At approximately day 1

Zona pellucida begins to appear in granulosa cell-engulfedt oocytes.

Reference [PubMed Link]

Rabinovici J, Jaffe RB. 1990. Development and regulation of growth and differentiated function in human and subhumand primate fetal gonads. Endocrine Reviews 11(4):532-557.