1 70 BRITISH LEPIDOPTERA. 



of Arheilgen tells me that he once found several larvae on black poplar early in June, 

 which were in all respects like the ordinary larva of the poplar-hawk, but which 

 pupated when they were scarcely half the usual size, and produced imagines the 

 same summer which completely agreed with Esper's figure. Late in the autumn of 

 1783 I likewise found on aspen such a larva, which had scarcely reached half the 

 normal size when it pupated ; I kept the pupa successfully through the whole winter, 

 but it unfortunately perished through an accident towards the spring. Might not 

 one conclude, from these corroborative observations, that this so-called variety is a 

 distinct species ? I will not decide at present, but await more precise observations. 

 This autumn I have again obtained several poplar-hawk larvae, which for the most 

 part have pupated at half size. Perhaps they will produce similarly varying moths. 

 I will make known my experience in the supplements to the following parts of this 

 work." In 1793 (Rhein. Mag., p. 649) he adds: "The so-called small obsoletely 

 marked aberration of Sph. populi, which I have made known in the N. G. d. eur. 

 Schm., ii., p. 181, has now been repeatedly bred in both sexes by an accurate and 

 observant young entomologist, Herr von Schenk, who is at present studying at 

 Giessen. Every time he has found the larva only on aspen. It was only half as 

 large as the ordinary larva of Sph. populi, proportionally somewhat thinner, and the 

 moth agreed entirely with Esper's figure. If it is really a separate species, one might 

 Dfime it Sph. tremulae.'''' 



Koch worked out somewhat unsatisfactorily the history of this 

 aberration (Schmett. S.-W. Deutsche p. 51) and gives the following 

 summary : This aberration was first figured by Esper (Die Schmett., 

 ii., pi. xxii., fig. 2), who gives a very reddish figure of it, whilst 

 he describes it (p. 52) as ' unicolorous light grey.' Borkhausen 

 (Sys. Besch., ii., p. 181) cites Esper and adds that Scriba 

 also has bred this aberration from the larva. In his Rhein. 

 Mag., p. 649, he repeats this and says further that Herr 

 von Schenk has also repeatedly found the larva on aspen and 

 bred both sexes. On account of the foodplant he gives it the 

 name tremulae. Meigen gives the following very correct description : 

 ' The moth is quite uniform light-grey, only the hindwings have 

 at the base a scarcely noticeable rust-coloured spot.' Ochsenheimer 

 only knew tremulae from Esper's defective figure. Treitschke 

 mentions (Die Schmett., vol. x., part 1, p. 140), that Herr Zetter has 

 discovered this great rarity in the neighbourhood of Moscow. 

 Zetter sent 3 specimens to Vienna, one of which remains in the 

 Royal Nat. Hist. Cabinet. [Koch then goes on to say : "Zetterstedt, 

 evidently thus erroneously named above, takes a newly dis- 

 covered (near Moscow) species for the true tremulae. This 

 can only be the one which Mann has diligently copied 

 from the specimen in the Royal Museum at Vienna. Zetterstedt 

 wrote his Faun. Ins. Lapponica in 1840 ; thus the priority-right 

 of the name tremulae belongs to Borkhausen, not to him ; 

 moreover, Borkhausen described a moth which occurred at Giessen, 

 not at Moscow. In any case he [Borkhausen] did not at all know 

 Zetterstedt's insect, for his tremulae is ' quite unicolorous light-grey,' 

 while Zetterstedt's — at least according to Herrich-Schaeffer's figure 

 (Bd. ii., Taf. iv., fig. 12)— is certainly far from light-grey, and shows 

 altogether quite a different species. If only some degree of attention 

 had been given to Borkhausen's description, his tremulae would 

 certainly not have been united or confused with Zetterstedt's." 

 This confusion of names tends to obscure the facts somewhat, 

 Koch having mistaken Zetter's name for a contraction of that 

 of Zetterstedt.] Koch then says that in order to become 

 acquainted with the puzzling tremulae, he asked several friends 

 in Giessen, who collected lepidoptera, to look out for it, and 



