The interesting experiments of Mr. Edwards are here principally introduced because they show how many weighty questions in connexion with seasonal dimorphism still remain to be solved. The present experiments do not offer a _direct_ but, at most, only an _indirect_ proof of the truth of my theory, since they show that the explanation opposed to mine is also in this case inadmissible. Thus we have here, as with _Papilio Ajax_, two out of the four annual generations mixed, _i.e._, consisting of summer and winter forms, and the conclusion is inevitable that these forms were not produced by the _gradual_ action of heat or cold. When, from pupæ of the same generation which are developed under precisely the same external conditions, both forms of the butterfly are produced, the cause of their diversity cannot lie in these conditions. It must rather depend on causes innate in the organism itself, _i.e._, on inherited duplicating tendencies which meet in the same generation, and to a certain extent contend with each other for precedence. The two forms must have had their origin in earlier generations, and there is nothing against the view that they have arisen through the gradual augmentation of the influences of temperature. In another sense, however, one might perceive, in the facts discovered by Edwards, an objection to my theory. By the action of cold the form _Umbrosa_, which flies in June, was produced. Now we should be inclined to regard the var. _Umbrosa_ as the summer form, and the var. _Fabricii_, which emerges in the autumn, hibernates in the imago state, and lays eggs in the spring, as the winter form. It would then be incomprehensible why the var. _Umbrosa_ (_i.e._, the summer form) should be produced by cold. But it is quite as possible that the var. _Umbrosa_ as that the var. _Fabricii_ is the winter form. We must not forget that, in this species, _not one of the four annual generations is exposed to the cold of winter in the pupal state_. When, therefore, we have in such cases seasonal dimorphism, to which complete certainty can only be given by continued observations of this butterfly, which does not occur very commonly in Virginia, this must depend on the fact that the species formerly hibernated in the pupal stage. This question now arises, which of the existing generations was formerly the hibernating one--the first or the last? Either may have done so _à priori_, according as the summer was formerly shorter or longer than now for this species. If the former were the case, the var. _Fabricii_ is the older winter form; were the latter the case, the var. _Umbrosa_ is the original winter form, as shall now be more closely established. Should the experiments which Mr. Edwards has performed in the course of his interesting investigations be repeated in future with always the same results, I should be inclined to explain the case as follows:--