NOTES ON THE VARIATION OF SPILOSOMA MENDICA. 187 



an isolated spot in one of the southern Alpine valleys where the white- 

 nialed variety is also found, although its habitat is there confined to a 

 few square kilometers ; he does not seem to be aware of its occurrence 

 in Ireland. The true home of var. rmtica is stated to be the Caucasus, 

 and the author suggests that its centre of distribution may hereafter 

 turn out to lie farther east or south of the Caspian. M. Caradja sug- 

 gests that, according to the law which holds good in the geographical 

 distribution of plants, this island-like occurrence of var. rustica in the 

 middle of districts inhabited by the ty^je points to the conclusion that 

 in the past it was the predominating or even the sole existing form, 

 and that its more limited distribution to-day is due to the type being 

 better jorotected by its darker colour. Further, seeing that on the 

 margins of the districts which it now inhabits there must be frequent 

 crossings between it and the type, he thinks that its entire disajDjjear- 

 ance from Europe is only a question of time. In support of the 

 opinion that the dark-maled type has developed from the white-maled 

 form, he refers to the cases of Amphklasys betularia var. double day aria 

 and Psdnra monacha var. eremita. The author seems, however, to think 

 that, where the white form still holds its own, white may really be the 

 best protective colour for it, seeing that it occurs at a time when the 

 ground is littered with the white petals from the fruit trees. On one 

 occasion a specimen settled at his feet in the garden, but he was entirely 

 unable to discern it among the fallen petals, and was actually going to 

 remove it with the petals, which he was clearing away in order to find 

 the moth. He concludes that the white variety is better adapted to the 

 dry (or cold) Continental climate of Moldavia, Bucovina, and the 

 Caucasus than the type, which seems to have sprung up in ocean- 

 bordering districts. 



It may be well here to glance at our common species of this genus 

 as a whole. Spilosoma menthastri shows but little colour variation in 

 southern Britain, being almost pure white with black dots in both 

 sexes. As, however, we travel north and west colour variation sets 

 in, and distributed over northern England, Scotland, and Ireland (so 

 far as I have obtained specimens) is a buff race known as var. ochracea, 

 White, which has, moreover, as I have noticed in my bred si^ecimens, a 

 tendency to become smoky coloured if ever so slightly crippled. Both 

 sexes, however, thus become yellower, and the variation does not tend 

 in the direction of sexual dimorphism. 



S. luhricipeda is an interesting species, inasmuch as even in our 

 southern English counties it keeps the buff colour which S. menthastri 

 only takes up in Scotland and Ireland, and locally in northern England. 

 But even then the colour is higher and deeper in the damper districts, 

 as in the western Highlands and certain parts of Ireland. In spite of 

 this, however, there is a distinct sexual difference of tint, the yellow 

 aiid buff of the males being mucli brighter than is that of the females, 

 but this sexual difference is less marked in southern and eastern England 

 than elsewhere. 



Now, it is very remarkable that it is just in those areas where the 

 sexual difference of S. luhricipeda is least marked that the sexual 

 difference of S. mendica is most strongly accentuated, the latter occur- 

 ring, however, and showing but little difference from our southern 

 specimens, in Aberdeenshire. The tendency in this latter species has 

 been to produce a wliite female, less pigmented probably, certainly 



