THE PYRAMEID GROUP OF VANESSIDS. 65 



plainly suggest that they had developed from separate swarms of 

 the prototype, which once must have flooded the lands from some 

 northern centre. But I think P. viifrinna certainly proves that the 

 atalanta-fonw tendency is strongly inheritent also in the ranliii-iovm. 

 group. If, in fig. 4, one covers up the light inner marginal spot in 

 the central area, and in fig. 8 the light median band with one's finger- 

 tips, both wings (in nature also in the matter of colour) at once 

 look as though they belonged to an aberration of /'. atalanta. 

 Another phylogenetic aberration of P. cardid, which came to my 

 notice at a time when, unfortunately, I placed no value upon it, is 

 transitory to P. terjmcltore of Chili in the underside facies of the 

 hindwings, and, perhaps, is a progressive form ; of the row of ocelli 

 in the outer area, only the two that are favoured already in light 

 specimens of P. cardid (fig. 9) were beautifully marked, the others 

 had disappeared, leaving only three white discs (as in P. terpsicJiore) to 

 mark their places in the ground colour, which was much lighter than 

 usual. 1 cannot go farther in my description to-day, as no specimen 

 of the kind is in my possession at the moment. Extreme cold or 

 extreme heat produce the symptomatic form ab. eh/iiii, Rbr. (in 4 per 

 cent, or more of the pupje). Direct sunshine acts like artificial heat or 

 cold, and the bred specimens are like those (rarely) captured in the 

 field. These results, demonstrating the sensibility of P. rani id to the 

 influence of light and temperature, stand apparently in direct contra- 

 diction with the remarkable facial constancy evinced by the species in 

 nature under all possible climatic conditions, in which a butterfly 

 can exist. Hopeless as the antagonism of facts may appear, the 

 harmonising solution to the problem comes of itself, when it is 

 remembered that (1) P. cardid. is by nature a polygoneutic species 

 belonging to the tropical or subtropical regions ; (2) being a 

 tropical species it is not accustomed to hybernate, and is, there- 

 fore, easily destroyed by any long period of cold ; that (8) for the 

 latter reason it cannot propagate its kind for any length of time in 

 localities where the winters are occasionally severe ; (4) therefore only 

 the notoriously migratory habits of P. cardiii explain the constant 

 recurrence of the species in countries with well-marked seasons, such 

 regions being dependent on a constant renewal of their stock from the 

 south. All this, now, implies nothing less than that, under natural 

 conditions, the climatic extremes to which the species subjects itself 

 by migration have not time to take any considerable effect, as they 

 only act on one generation (in Lapland where the specimens could 

 never survive the winter), or, on two, three, or more generations in 

 Central Europe under favourable conditions, when, however, th& 

 specimens would not remain, but would press on till they perished in 

 the sea or in the cold of a northern winter. But, if a group of 

 the species belying the migratory habit were inclined to stop and 

 accommodate itself to northern conditions, or in the south to develop 

 a special "mountain form," even then there would be little or no 

 chance of climatic variation within that group, because any budding 

 varietal, or even non-migratoiy tendency, would be simply "swamped " 

 by the continuous influx of typical migrants, before sexual alienation 

 had even a chance of development to prevent this. Evidently, only 

 when local isolation assists the local climatic factors by (1) giving 

 them time to act, and (2) allowing the effects of that action to be 



