( 518 ) 



forms, so that the distiuguisLiug cLaractei-s eau accumulate iu spite of the occasional 

 immigration of specimens of the old stock. As we shall have to deal with this kind 

 of ])hysiological selection, which in fact is a kind of sexnal selection, in another jilacc 

 when treating upon the variation of glandular organs in Le/julopteru, we do not now 

 enter upon a discussion of that factor. The variation of Lepldopteni explained in 

 the present paper points, however, to a further factor being active, the importance 

 of which as a means of prevention of intercrossing has been recognised as far back 

 as 18411, and we shall try now, on the ground of our researches, ti> estimate tlie 

 influence of geographical polymorphism in the sexual organs upon tlie divergent 

 development of the Lepidoptera. 



C. Mechanical Selection. 



The genital armature of Lepidoptera has the function of a special prehensile 

 apparatus during copulation. As such apjiaratus is found in all Lepidoptera, we can 

 conclude that its function is of high importance for the act of copulation. When, 

 however, a physiologically important organ is found to be of a different structure in 

 every two species, it is likewise correct to conclude that the difference in the 

 structure has some physiological significance. Hence we think that the inference 

 to be drawn from the fact that the copulatory organs are different in different species 

 has to be that the siiecialisation iu structure means a specialisation in the function 

 as prehensile organ — i.e. that, as with the help of the apparatus the male has to take 

 a hold on the female and the female on the male, the organs of the sexes of the 

 same species are best adapted to each other. This inference implies that specimens 

 of diverse species can less easily copulate than specimens of the same sj)ecies, and 

 that there might be cases iu which copulation between different species would be 

 impossible in consequence of the highly divergent specialisation of the organs of 

 copulation. A similar view has been held by the earlier writers on the subject, 

 Siebold* and Uufour, f the latter giving expression to his opinion in the well-known 

 sentence that " Varmure copulatrice . . . est la garantie de la consercation dex types, 

 la sauve(/arde de la legitimite de Vespece." 



The different development of the organs of copulation is here alleged to be 

 a means of i)reventiou of intercrossing between specifically different specimens, and 

 the same has more recently been said by Escherich,| noffer,§ and others. Thougii 

 we know from experience that Escherich's assertion that an effective copulation 

 between diverse species is never possible is erroneous, and that therefore Verhoeffll 

 is right in rejecting this ])art of Escherich's theory, it remains nevertheless evident 

 that under the premiss that the male and female of one sjiccics really are a(lu])ted 

 to each other in respect to the genital armature, specimens which are not adajited to 

 each other cannot so easily imite in copulation, and that even when a union is 

 effected the penis will sometimes be prevented from entering the vagina iu con- 

 sequence of the vaginal armature, to which tlie organs of that male are not adapted, 

 being a mechanical barrier. Before, however, this conclusion can be accepted, 

 it has to be ascertained whether the actual structure of the female and male genital 

 armature is in accordance with the above i)remiss. 



Gosself was quite rigiit in expecting to find that "every peculiarity in the 



• Vrrgl. Anat. Berlin, 184S. § 354. note 1'. ^ Mitth. Nat. Vir. Steirrmai-lr. 1888. 



t Ann. Sc. .Xat. (H). I. 18<4. p. 253. ]| Knt. Xachr. 1893. p. 44. 



X Verh. z. b. 6e». 1I'(V«. 18'.I2. p. 234. ^ Tram. Linn. Svc. Land. (2). II. 1883. p. 279. 



