It is generally understood, I believe, that to get eggs the requisite plant must be also enclosed in the gauze bag with the female insect. Such is often, but not always the fact, and it will lighten the labours of the biologist and simplify his methods if a more correct statement be made. That one genus of butterflies should not use or require living plants to receive their eggs, while others will fret and die without ovipositing if their peculiar plant be withheld, indicates a relationship, or gives a hint as to grouping of genera upon natural lines.