SEASONAL POLYMORPHISM. 127 



required. In Ehopal. Pal. I have pointed out several striking Asiatic 

 races, but, concerning Europe, I have not gone far beyond illustrating 

 what was already known. Since then I have published some notes in 

 the Linnean Soc. Jonrn. of May, 1913, on the Linnean specimen and 

 on the southern rulf/aris, Vi'ty., in the Ent. Rec. of April, 1916, in- 

 cluding a description of two British races, and in that of December, 

 1921, describing an Italian one. In June, 1920 {Boll. Lab. Zool, 

 Sciiola Af/ric. I'ortiri, p. 52), I made some remarks on vieridionalis, 

 Eiihl, and on the misuse, which is so generally made, of Esper's name 

 of napaeae. I think I can now venture an attempt at drawing out in 

 very broad lines the geographical and seB,sonal variations of P. napi in 

 Western Europe, although a great many gaps must remain, to be 

 filled in future. 



The generation which emerges from hybernated chrysalids, whether 

 of the single- brooded races or the first of the double- or triple-brooded 

 ones, is by far the most variable, both individually and geographically, 

 and the most abundant, as a rule. This explains why it has been 

 worked out more. There are several features which vary considerably 

 and their various combinations are so complex that for a long time I 

 thought it was hopeless to try and classify the innumerable individual 

 forms, so as to show how they stand to each other and make out the 

 main and the collateral lines of variations. These remarks apply 

 especially to the upperside of the female, which exhibits all the 

 characters much more prominently, although they are fundamentally 

 the same as those of its underside and of both surfaces of the male. 

 For this reason I shall make use of the former in the following study, 

 it being understood that the two latter usually follow on a minor 

 scale, except when especially stated. It was only when I had made 

 out the key to the main line of variation in the genus Zj/f/aena, des- 

 cribed in my papers on Z. /ilipendidcie, L. {Ent. Rec, 1921, p. 105), 

 and on Z. }>i(rpi(rali!<, Briinn. {I.e., 1922, p. 30), and I had noted its 

 remarkable resemblance to that of the Pie rid i in general and of P. napi 

 in particular, as stated in the first of these papers, at page 107, that I 

 was able to unravel the variation of this species. In this case, as in 

 that one, it is a question of noticing and bearing in mind all through 

 that there are two sorts of wing-markings : the nervular suffusion or 

 pattern and the true or transverse pattern, which can vary in extent 

 independently of each other, according to surroundings. Dampness, 

 of course, increases the extent of both, but cold and dampness develop 

 the nervular pattern, whilst heat and dampness develop the true or 

 transverse pattern, as much as the specific capacity, so limited in napi, 

 will allow the latter to develop, considering it only consists in a series 

 of spots across the middle of forewing, one costal spot and a series of 

 thickenings, equivalent to these, sometimes detectable on the dark 

 streaks of the underside of hindwings, and in the thickenings at the end 

 of the nervules on outermargin, which may blend at apex into a 

 crescent and then extend to a triangle, especially when the latter 

 blends also with the first, or costal, of the spots mentioned above. 

 One finds evidence in this and other Pieri<li that the dark streaks on 

 the terminal part of the nervures may be either of nervular or of inter- 

 nervular origin (blending of the two centers placed on each side of 

 nervure) or still more often of a mixture of both, in the same way as 

 the marginal band of the Zytjaenae. The independent development of 



