99 



considerable, and at last the outcome of the derived forms on 

 the two continents is distinct, the late descendants being parted 

 by specific differences. How an aberration leads to a permanent 

 variety ; how insulation produces permanent varieties ; how a 

 variety becomes a species, breeding true, not subject to reversion, 

 and adapted by change of habit to altered circumstances 



Note. — Since this paper was put to press, I have received 

 from Dr. Staudinger 2 S and 2 ? of Lapland Bryonm. 



One of the males has the nervules and branches of under side 

 of secondaries bordered with brown in same manner as the 

 Alpine examples spoken of; but the other has an excess of the 

 brown edging, so that nothing of the ground color of the wing is 

 seen except a narrow stripe in cell and streaks in the interspaces 

 of the nervules. In this respect this example resembles Hiilda. 



Note on Plates. — These were drawn and printed in London, 

 and no opportunity for correction of errors could be given. Figs. 

 7, II, and 13 would represent the forms as having black spots on 

 under side of primaries, contrary to the statement of the text. 

 The artist has mistaken discoloration caused by the transparency 

 of the wing, and only apparent when held to the light, for spots ; 

 but in all these butterflies the surface is absolutely free from 

 black scales at the points indicated, and is white or yellow, 

 whereas in Napi and Napace the black spots of underside are 

 caused by black scales laid on. 



Description of Plates. 



PLATE 2. 



WINTER FORMS. 

 European. 



1 . BryonicB (Alps) $ 



2. Napi (Germany) ^ 



3. NapcBce " ? 



American. 



4. Bryonice (Newfoundland) .. .. ? 



5. Hulda (Alaska, &c.) ? 



6. Venosa (California) $ 



7- " " ? 



8. Oleracea hye malt's (New York). . i 



9. Borealis (Anticosti) $ 



PLATE 3. 



SUMMER FORMS. 



American. 



10. Acadica (Newfoundland) $ 



"• " " ? 



12. Pallida (Vancouver's Island).. $ 



13. « « " ..? 



14. Castoria (California) $' 



15. Oleracea cestiva (New York). . . $ 



16. " •' " ... $ 



17. Virginiensis (Coalburgh.W.Va. ? 



18. " " " . <5 



