I ran across these Japanese Nest Egg Gourds that were used as nest eggs to encourage egg laying that were popular in the 1880s. They are white and about the size of a hen's egg.
http://rareseeds.com/vegetables-d-o/gourds/gourds/japanese-nest-egg-gourd-13494.html
http://rareseeds.com/vegetables-d-o/gourds/gourds/japanese-nest-egg-gourd-13494.html