29 



helive we have no fixed recurrent varietal forms, but a Lost of trivial 

 aberrations; thus, there may be considerable variation in the tone 

 of the yellow ground colour, which in some individuals is much 

 lighter than others. It was to a small-sized individual of one of 

 these lighter forms that Stephens erroneously gave the name of 

 c/iri/sot/ii'iiic.^* Indeed, the colour varies from a rich deep orange to 

 almost sulphur, and occasionally one meets with a blending of the 

 two tints in one individual, as in the case of a typical orange speci- 

 men with a sulphur line along the costa, and so forth. Then there- 

 is a good deal of variation in the size and shape of the black spot 

 on the disc of the foi-ewings, and in the amount of the blacl\ suffu- 

 sion at the base, which in some specimens extends practically over 

 the whole of the wings ; also in the width and intensity of the black 

 borders, and occasionally the hindwings have a distinct pink flush. 

 In the female there is very great variation in the amount of yellow 

 spotting in the black borders, specimens occurring rarely in which 

 the borders are practically immaculate ; but these all appear to me 

 to be mere accidental aberrations and not to have any bearing upon 

 the status of the species in this country. 



Although I have been able to adduce little that is new, such frag- 

 njents as I have been able to strmg together appear to suggest that 

 without immigration C. etiiisa would soon be extinct in J^ritain ; 

 that in the countries nearest to the east of us the species has little, 

 if any, better chance of continuous existence than here, and that 

 any reinforcement of our stock must come from more southern 

 climes. We need not tax our credulity to the extent of imagining 

 individuals rising from the sunny coasts of Algeria and alighting 

 on our inhospitable shores ; there are many warm valleys in southern 

 France and Spain where swarms might originate, and once on the 

 move easily reach us by some such routes of migration as already 

 suggested. Or if, as there is some evidence, insects on migration 

 rise to great heights,'''^ and are borne involuntarily on the upper wind 

 currents, who can say from how great a distance they might come? 

 Then there is also the possibility, although I do not know^ of any 

 evidence to support the suggestion, that migration may be progres- 

 sively carried on through several succeeding generations. For 

 instance, if an early spring brood in the southernmost haunts of the 

 species commenced a northern movement, it might be continued by 

 successive generations through a whole season, without the species 

 exceeding the limits of the area in which it thrives ; each genera- 

 tion, by reason of the introduction of fresli blood as it proceeds on 

 its course, gathering force, so that at the final movement beyond 

 the area, the species would be at its greatest strength, thus allowing 

 of an enormous number of individuals setting out on the final 

 migration to the districts of its casual distribution such as northern 

 Europe and Britain. 



s' Steph. " 111.," vol. i., p. 11, pi. ii., figs. 1 and 2. 



3'' See Flusia f/ainma, "Proc," 1890, p. 77. 



