Green’s Dictionary of Slang

generation box n.

the vagina.

c.1702

‘New Irish Christmas Box: Or, The Female Dear joy trick’d out of her Maiden Head’ in Ebsworth Bagford Ballads I (1878) 75: [He] who hath Approached the Tabernacle, and broke open the Generation-Box, of our Dear Sister Tabitha, a Daughter of the Light.