222 A CATALOGUE OF THE LEPIDOPTERA OF 



Augusti." Again, Duponcliel, in his " Catalogue Metliodique" 

 (1846), assigns the same two months. M. Bruand, who has 

 done much towards the natural history of the Lepidoptera in his 

 valuable " Catalogue des Lepidopteres du Department du 

 Doubs" (1846), states the same months as the time of its ap- 

 pearance there. De Graaf, in Herklot's " Bouwstoffen vor eene 

 Fauna van Nederland" (vol. 1, p. 221, 1853), gives May, and June, 

 and August, and September, for its flight in South Holland. 

 Treitschke, who may be said to speak for Austria and Germany, 

 in his " Hulfsbuch" (1833), gives August and September. 

 No doubt the time of the second brood. Eversmann, in his 

 " Fauna Lepidopterologica Volgo-Uralensis" (1844), states that 

 about Casan (55° N.L.) June and July is its time on the 

 wing; and Dalman, in his clever " Forsok till Systematisk 

 uppstallung af Sveriges Fjarillar" (K.V.A. Hand. 1816), 

 observes: " Hab. apud nos rarius. Prope Upsalium, &c., mihi 

 obvius mensibus Junio et Julio." Of our British authors, 

 Haworth I. c. says end of May and middle of July; and Ste- 

 phens /. c. beginning of June and middle of August. Mr. 

 Stainton says May and August. Apparently, therefore, we 

 have have two distinct seasons for it, though Mr. Bond informs 

 me he has met with a few specimens in the intermediate months ; 

 but M. Guenee, to whose authority we must all submit, in his 

 admirable introduction to the 9th vol. of his " Species general 

 des Lepidopteres," just from the press, on this point says: 

 " Quant aux doubles generations, si souvent affirmees ou de- 

 menties par les auteurs, elles restent, comme dans les autres 

 divisions subordonnees a la latitude, et souvent aussi a la tempe- 

 rature variable de certaines annees. Ce serait done un tort d'y 

 attacher une tres grande importance." This source of difference 

 need not therefore raise any difficulty as to the insect being 

 identical in all its localities. It may not, however, be unin- 

 teresting to state that, if we draw an isothermal line of 51 

 degrees across the map of Europe, we seem to separate the single 

 from the double broods by its track. On the south of such a 

 line we shall find Bristol, London (507°), South Holland (Brus- 

 sels, 50-4°), all France, and Vienna (50-2"), the region of the 



