In studying the seasonal variation exhibited by various species of butterflies, I have been struck by the fact, that whereas in most instances the form emerging in the spring is darker and smaller than the summer brood, there are also exceptions to this rule, in which the vernal emergence is the lighter. Take, for instance, the genus Pieris. The vernal broods of P. napi and P. protodice are distinctly more dusky than those which have undergone their whole metamorphosis in a single season; but, on the other hand, the spring emergences of P. rapœ and P.brassicœ are wont to be pale, and the spring-emerging P. virginiensis is pale, and as Mr. W. H. Edwards remarks (“Papilio,” 1881, p. 97), more like the summer than the winter form of tis progenitor P. napi.