It is not, I believe, generally known that, closely as these two insects resemble each other in the larval and pupal states, they may, nevertheless, be readily and invariably distinguished by the constant differences in the anterior horns of the former and in the hump of the latter. I was fortunate enough, the present summer, to have several larvæ of each species feeding, as also several pupæ of each hanging, at one and the same time ; and with the exception of the characters here given, I do not think there are any other distinguishing features to be relied upon.