Among a number of cocoons of the family of Bombycidæ collected on Long Island this autumn, I have one of P. cecropia of light weight. As the examination of this cocoon revealed conditions unknown to me, I have thought it desirable to make a record for your invaluable journal. The absence of the loose silk of a reddish hue which characterizes the appearance of the new made cocoon, indicated that it was a manufacture of the previous year. On opening it I found within a cocoon of O. macrurum, the parasite that commonly attacks the Potyphemus caterpillar. The parasite had emerged from its cocoon, as evidenced by the usual lid opening at one end, and had escaped into the outer air through the open passage that exists in the cocoon of the moth.