258 BRITISH LEPIDOPTERA. 



We suspect that this failure to emerge rarely happens in nature, 

 at least pupae that have spun up singly and with an abundance of 

 room, among their foodplant have not been noticed so to fail. 



Dehiscence. — No part of the pupal skin is detached on 

 dehiscence ; it splits between the meso- and metathorax and between 

 the fore- and hindwings as far as the end of the 3rd abdominal segment, 

 also along the median line of the meso- and metathorax to the 

 face-piece ; the fission then continues between the prothor'ax and the 

 face-piece and between the antenna- and wing-cases for about half the 

 length of the former (Bacot). 



Extended duration of pupal stage. — It is a very common 

 thing for this species to pass more than one winter in the pupal 

 stage. Fritsch notes pupae as frequently going over two winters, 

 and remarks that, in one instance, an 1833 larva produced an imago 

 in 1838, whilst Fenn records {Ent. Rec., ii., p. 90), on the authority 

 of Tester, a pupa going over five years before the emergence ot 

 the imago. Tugwell notes 1881 eggs (Rannoch) producing 7 $ s 

 and 1$ in 1882, and 6<?s and 7 $ s in 1883. Buckler says that 

 of a dozen pupae, formed in 1881, no imagines appeared in 1882, 

 and only 3 were bred in 1883. (For several other instances see postea, 

 pp. 261 et seq.) Adkin observes {Ent. Rec, ii., p. 90) of two different 

 batches in which the greater number of imagines emerged 

 in the second year, that, whilst in one batch, those that lay over 

 until the second year were all males, and all except one that 

 came out the first year were females, in the second batch 

 males alone came out the first year and females the second year. 

 A little judicious forcing at the end of February and early March 

 will bring out almost all the imagines that are ready to emerge, 

 and reduce the percentage of deaths, although it cannot possibly affect 

 any pupae that are going over to a second year.* The difference 

 in the temperature of a cold greenhouse and a kitchen mantelpiece is 

 often quite sufficient {vide, Ent. Record, iv., p. 79). Chapman notes as 

 to this: " On January 1 8th, 1902, pupae of D. versicolora contained 

 fully developed imagines, or were still in the milky stage ; the 

 developed imagines were quite ready to emerge, except that they 

 were still bathed in fluid, and the tracheal linings were not fully 

 loosened ; breathing might be difficult did this happen till the last 

 moment — at any rate so it was." 



Foodplants. — Birch, alder (Reid), Betula alba, Salix caprea 

 (Lambillion), Coryhis avellana f (Borkhausen), Carpi/ins bctulus, 

 Tilia europaea (Ochsenheimer), sallow (Favre). 



Parasites. — Frings records (Soc. Ent., xi., p. 171) opening a 

 pupa and finding in it a fully developed £ , which could not have 

 been dead more than two days, but whose abdomen contained a 



* Chapman notes : "In view of my observations on Lachneis lanestris (Ent. 

 Rec, xiii., pp. 284, et seq.), there is no doubt, I think, that forcing in February and 

 March will bring out those that meant to come out, and which probably began to 

 get read)' to do so in October or November, and may save them from dying instead, 

 but will have no effect whatever on those that are going over, since no development 

 has so far taken place in them." 



f Borkhausen says (Rhein. Mag., i., p. 327) that as birch and alder do not 

 keep well in water, he has reared this species, and also Notodonta dromedarius, 

 Brephos parthenias, &c, on Coryhis avellana, and has been quite successful, even 

 when rearing them from the egg. 



