ON THE CAUSES OF VARIATION. 495 



find her, or to mate with her, and particularly the antennse, eyes, 

 and genitalia, are profoundly modified and complex. This is 

 especially noticeable in the Psychidm, where the female remains 

 in her case, a mere mouthless, eyeless, legless, and wingless grub, 

 and the male has most complex and ramose antennse and complex 

 genitalia. Another remarkable instance may be cited in the 

 Lampyridm, 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 antennse in the male, until at 

 last, in the Pliengodini, 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 modifica- 

 tion offers for union, than upon sexual selection in its proper 

 and restricted sense. 



In this category must also be included the influence of philo- 

 progeneity, 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 Lepidopteraj or in modification of various other 

 parts of the body exhibited in various orders of insects to facili- 

 tate 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 Prorvuha, where the ovipositor and the maxillse 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 ex- 

 plained 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. 



Hybridify.— 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 



