24 THE ENTOMOLOGIST. 



wings being wholly irrorated with dark brown. On the upper 

 side of the fore wings the median puncta, as well as the inner 

 marginal blotch, are obsolete. 



The costal blotches are united, as in V. urticce ab. atrehateiisis, 

 Boisd., or in extreme forms of V. io ab. helisaria, Obth. 



Held against the light the wings are much less transparent 

 than in typical urticce, and therefore approach in opaqueness 

 the wings of V. io. The long slender shape of the wings appears 

 also in aberrations of V. io. The antennae, instead of l3eing 

 chequered with black and white, are uniform brownish in colour, 

 and therefore more like those of V. io than of V. urticce. 



I had exposed the pupa of this io-form aberration, together 

 with some others, during three days after pupation to tempera- 

 tures occasionally as high as 48° C, in the endeavour to strike 

 at and impair the "fixed" hereditary tendencies before these 

 should have found time to determine the facies on the usual 

 pake-form lines.* Afterwards the pupae were climatized in 

 almost tropical conditions, so as to further influence any new 

 lines of development which might be in progress, in the hope of 

 immediately effecting such a high degree of change in the facies 

 as would by the only other possible method— that of utilizing 

 the hereditary forces — take years to attain. 



When the imagines ultimately emerged I found that only 

 two had defied hereditism during pupal development ; they were 

 the last to emerge (after ten days), and one was the io-form 

 aberration described. On the rest of the pupae hereditism had 

 in a great measure retained its hold. The specimens were only 

 slightly io-form, being more or less transitory in markings and 

 colour to the Corsican variety ichnusa, Bon., and to the Asian 

 form cliinensis, Leech, transitions to the all-brown, irrorated 

 under side of the latter appearing in two of my aberrations of 

 urticce. 



'■^'' I suggest that the colours in the facies of a butterfly are greatly 

 dependent in their kind and distribution on the manner in which the 

 diffusion of the blood (pigment) into the wings is influenced by the pressure 

 on the blood from the vital process in the pupa. An aberration like that 

 described would have developed under abnormally high blood pressure, 

 following after a temporary interruption of the vital process by extreme tem- 

 perature. The overflow of black colour along the main ducts of the fore 

 wings is symptomatic of this, and tells of the overthrow of hereditary 

 tendencies, though the phylogenetic value of a specimen may in a sense be 

 impaired by such symptomatic details (which, by the way, besides an only 

 occasional infertility of the sexes, seem to offer the only and perhaps in- 

 sufiicient excuse for referring aberrations to teratology). I have already, in 

 my description of ab. iofonnis in the Ent. Eecord, pt. iv. 1909, tried to show 

 that these details may occur together with and be distinguished from pio- 

 gressive or atavic features of the facies. It is, however, often a very compli- 

 cated and even impossible matter to separate such features, because when, 

 for instance, an urtic ce-ahermtion is facially transitory to V. io, such a facial 

 detail as the absence of the median puncta on the fore wings is at once 

 symptomatic, progressive, and atavic. 



