find her, or to mate with her, and particularly the antennæ, eyes, and genitalia, are profoundly modified and complex. This is especially noticeable in the Psychidæ, where the female remains in her case, a mere mouthless, eyeless, legless, and wingless grub, and the male has most complex and ramose antennæ and complex genitalia. Another remarkable instance may be cited in the Lampyridæ, where we find every degree of degradation in the female, from partial wings to no wings at all, accompanied with increasing complexity of eyes and antennæ in the male, until at last, in the Phengodini, the female is so larviform that she can hardly be distinguished from the true larva. In all these cases the female has been as profoundly modified as, and often more so than, the male, and in the latter case a phosphorescent power has been evolved so that the attractiveness, as in the human species, is rather on the female side. Again, in the case of Corydalus, in Neuroptera, the profound modification of the jaws in the male into prehensile, sickle-shaped organs is to be explained rather on the interaction, between the sexes, and the facility the modification offers for union, than upon sexual selection in its proper and restricted sense.
In this category must also be included the influence of philoprogeneity, which has modified the female rather than the male either in the primary sexual organs for offense or defense, as in the sting of the aculeate Hymenoptera; or in the secondary sexual characters, as in the anal tufts of hair, secretory glands, etc., of many Lepidoptera; or in modification of various other parts of the body exhibited in various orders of insects to facilitate provision for their young, whether in the preservation of the eggs or the accumulation of food for the future progeny. A notable instance of how far this may be carried is furnished by the female Pronuba, where the ovipositor and the maxillæ are so profoundly modified as to make her unique in her order. Sexual selection can have little to do with these modifications, cases of which might be multiplied indefinitely; nor can they be fully explained by natural selection, in the restricted sense in which we have proposed to use it; nor by physiological selection.
In this category might also be included modification which has resulted in the various forms of females which obtain in the same species, fitted whether for agamic or sexual reproduction, and which are far more readily explained on the theory of sexual differentiation aided by environmental influence, especially food and temperature, than upon any other.
Hybridity.—The subject of hybridity has been fully discussed by many, and by no one more ably than by Darwin himself. It has generally been assumed that the hybrid of any two species is sterile, and, in fact, hybridity has been looked upon as one of
