VARIATION IN VANESSA URTIC^. 25 



In speaking of the biological significance which might under- 

 lie an io-form facies, appearing by saltation in a specimen 

 of urticcB reared from wild larvfe, it will be necessary to distin- 

 guish whether the present and future only or otherwise the past 

 history of such facial io-formity is under consideration. 



In the first case I suggest that the io-form facies, even if it 

 occurred and were developed to perfection in an isolated group 

 of icrticcB, would not be followed by physiological changes of such 

 a nature as would link the variety also specifically to V. io. 

 Unless it should be proved that a certain kind of facies is entirely 

 bound up not only with a certain kind of physiological structure, 

 but also with a certain sexual aflfinit}^ there is no reason to 

 assume tha^t facial ioformity also entails specific io-formity. At 

 present it would appear that every variety which becomes 

 separated from the type will within its own special group be 

 quite free to vary — for instance, in the structural details of the 

 sexual organs independently of the facies. Thus, while from a 

 locally isolated group of urticce an entirely new species, facially 

 resembling V. io, might be evolved, it would also be thinkable 

 that another isolated group of urticce had remained typical in 

 facies, but grew to a greater size, and became specifically distinct 

 from the type by extreme development of otherwise varietal 

 changes in the larval habits,* and especially in the female sexual 

 scent, male ancillary appendages, &c., of the imagines ; while 

 yet another (seasonal) group could have become completely 

 changed in facies, ioform again, for instance, and yet be 

 specifically unchanged.\ 



* Longer feeding-up time tinder the influence of cold, or not propor- 

 tionately accelerating the feeding-up time in a temperature higher than 

 normal, is well-known to be conducive to a considerable increase in size 

 (Elwes, Standfuss). This also explains why northern or southern forms 

 of some central European species are both often notable for conaparatively 

 great size. The climate on mountains sometimes has a similar effect. 



f Taken strictly, the scientific conception of "species" is based on, and 

 will accept no other evidence than that of, unlimited fertility (based in its 

 turn on sexual affinity) among the individuals of one group to mark them 

 " species." The transmittability of any special facies by hereditism is not 

 necessarily dependent on any special structural details of the genitalia, &c., 

 nor is the fertility of a specimen with an aberrative facies in any way im- 

 paired merely by the possession of that aberrant facies. Every breeder of 

 facial varieties by artificial selection testifies to this by his success. Also 

 Prof. Standfuss yz?'s^ proved in 1897 by pairing aberrant urticce obtained by 

 exposure of the pupse to low temperatures that the altered facies of a "tem- 

 perature form," resulting from an experiment with pupae from wild larvae, 

 is transmittable by progressive hereditism in a small percentage of the brood 

 even under normal conditions of temperature. The fertility of the specimens 

 was unimpaired. Therefore the aberrant facies produced by the effects of 

 temperature had («) become potentiallj^ inherent in the spermatozoa and ova, 

 (6) and this without necessitating an alteration in sexual affinity. Moths which 

 breed freely in captivity offer better proofs than the Rhopalocera. Thus the 

 best way to start breeding varieties siiccessfully from normal wild speci- 

 mens — for instance, of A. grossulariata — is to produce a few aberrations 



