ACADEMY OF SCIENCES. 167 



5. frigida. Scud. Like Napi, but with the whole of the lines a little 



narrower and fainter. 



6. Napi. Lines all very faint, almost obsolete as they approach 



(Colorado.) the margin. 



7. Napi. Lines still fainter, quite obsolete at the margin, with 

 (Massachusetts.) the ground color of the wings still yellow. 



8. pallida. Scud. Ground color usually white, sometimes pale yellow, 

 —castoria. Reak. with the lines bordering the nervules, very faint or 



quite obsolete, passing by many gradations into the 

 following : 

 P. oleracea. Veins without margins of scales, surface white or pale 



yellow. 



We may pursue this still farther, until we arrive at a form of oleracea almost 

 pure white, in which even the nervules themselves are scarcely to be traced 

 by any definite color. But the subject may perhaps be better illustrated by 

 retracing our steps, this time starting with oleracea, and endeavoring to show 

 its relationship to P. Rupee. 



1. P. oleracea. Almost pure white, with faint yellowish tinge beneath. 



c^ without spots. 



2. White, with very faint indications of spots on the 

 (Oreg. and N. Cal.) primaries. 



3. Castoria. Reak. White, with faint yellowish tinge. $ with faint spots 



on the primaries. 



4. Marginalis. Scud. White above, yellow beneath on secondaries, $■ with 



distinct spots on primaries, and with the apex slightly 

 dusky. 



5. Ergani. tf with the apex more broadly dusky, and with the 



(Europe.) spots on primaries well defined. 



6. Rapce. L. Apices broadly dusky. Spots very distinct and well 



defined. Underside of secondaries, white, greenish 

 white to yellow. 



7. Novanglws. Scud. Upper and lower surfaces yellow, spots and apices as 



in Rapa. 



Thus it will be seen, that according to my views, two branches of variation 

 have proceeded from the one original source, though what that original source 

 may be we are at a loss to tell, and that the most special characters distin- 

 guishing these two branches belong to P. Pallida, which in many respects 

 resembles P. Rapce as much as it does P. Napi. I am aware that there are 

 other points of difference between the extremes of these insects, but certainly 

 none more remarkable than between the darkly veined specimen of P. venosa, 

 and the almost immaculate and veinless examples of P. Pallida. 



Breeding the caterpillars through successive generations, will alone lead us 

 to the truth, and unhappily at present we know but little of the earlier stages 

 of these creatures. The present remarks must therefore be taken as a sugges- 

 tion rather than the dogmatic statement of a fact. 



Peoc. Cal. Acad. Sci., Vol. VII.— 13 



