( 435 , 



discriminatp between the various scents, and follow that scent which, to put it more 

 personally, incites them most. We have here a psychological selection. Now, if a 

 variation takes place in the organ of smell and in the scent-producing glands, it 

 seems to us evident that the effect will be such that the varietal individuals do not 

 follow the same scent as that to which the normal specimens give preference, but select 

 a varietal scent. (.'areful observations about psychological variation are extremely 

 scarce; but we can give a beautiful iUustration on the authority of Professor Standfus.s,* 

 who says that at Zurich males of CalliTnorpha domimda came very rarely to females 

 of the Italian variety persona, while they were attracted in great numbers by the 

 females of dominidd.. We see here that morphological and psychological variation 

 can go hand in hand. If the power of discriminating scent is so highly developed 

 throughout the order of Lepidoptera as in the case of Caliimorpha domimda, we 

 have a ready explanation of the phenomenon that the scent -organs, compared with the 

 colour and pattern of the wings, are so constant in Lepidojjtera. It is readily con- 

 ceivable that the relative constancy of the scent-organs of Lepidoptera is a con- 

 se(juence of psychological selection based upon the difference in the organ of smell 

 and in the scent-glands. And if we must admit the probability of the influence of 

 this kind of mental selection, we arejustified in concluding that psychological selection 

 takes place in all animals which have one or the other organ of sense highly 

 developed. As, however, wnih the various organs of sense only certain kinds of 

 characters are perceivable, it is obvious that in different groups of animals psycho- 

 logical selection will affect different sets of characters according to which organ of 

 sense lias a high power of discrimination. Thus it seems to us intelligible tliat there 

 exists such a strong contrast between Lepidoptera and birds in respect to the 

 constancy of colour and markings. The great variability in colour in the order of 

 Lepidopjtera and the relatively slight variability f in scent-organ.< can be accounted 

 for by the presence of selection as to scent-organs and the absence of selection as to 

 colour,J while the surprisingly great constancy even in the shade of colour among 

 birds may largely be due to the sharp eyesight of these animals rendering them 

 capable of distinguishing between shades of colour, and hence inducing them to 

 associate with specimens of their own colour and to drive differently coloured indi- 

 viduals awa}-. 



The effect of the variation of psychical qualities as dependent on the variability 

 of the organs of .sense can, like the variation of morphological characters, be 

 classified in individual, geographical, and historical iiolymorphi^m. The considera- 



* Standfuss, JIandhurh fiir Schmctterling.'isainmlfr. ^iiW.i, ls9(j. p. 107. 



t The scent-organs rif Lrpidojitera. especially those of the mah's, are not constant in every case ; there 

 .are even s])ecies in which they are very variable; and the colour of birds is also not constant in every 

 sjjecies. 



t Eimer, Artbililvmj und W-ru-andtscha/t liri Schmctterlim/en, tries to '■ prove " on the ground of his 

 studies on the wing-pattoin of Papilios that the transmutation of animated nature takes place without 

 natural selection. ISut even it'this be true as regards a direct effect of selection on the wing-pattern, it is 

 conceivable that psychological selection, which is a jiart of natural selertion, can have, besides the direct 

 influence on ''structural" characters, an indirect influence on the distribution of colour on the wings 

 Eimer is in so far rpiite right as he says with Darwin (not against Darwin) that incipient varieties cannot 

 have been oiiginated by natural selection ; where a '■ selection " takes place, there must already be a 

 difference amongst the individuals. As Eimer expressly says that natural selection cannot produce species 

 but only preserve species, and as, further, Eimer actually does not show how s|)ecies (conforming to Eimer's 

 definition of si)ecies) but only how varieties oiiginate, I cannot perceive why we should not attribute to 

 natural selection the preservation of nirirtnl characters. Variation is, according to Darwin, not the out- 

 come of natural selection, but is the premiss of natural selection ; vaiietal characters can be preserved by 

 selection and increased by survival of the fittest. I do not perceive any great contrast between Darwin 

 snd Eimer in respect to these points. 



