1909.] 



Two Races of the Moth Acidalia virgularia. 



137 



safeguarded him against any material error of judgment in the present 

 investigations. 



As regards the pure stock, or presumable homozygotes, inbreeding for 

 ten generations, under more or less artificial conditions, has not had the very 

 slightest influence on the pretty Hyeres form nor, in the aggregate, on the 

 London form. Excepting a single dark specimen, which was obviously an 

 accidental importation (perhaps on food-plant, as the moth is so common in 

 Mr. Bacot's neighbourhood), upwards of 400 specimens show not the slightest 

 deviation from the clean whitish ground-colour which characterises the Hyeres 

 race. The dark form, which varies more in a wild state, naturally showed 

 a greater range, and one or two broods, apparently by some accidental 

 selective agency, became lighter than the normal ; but here, again, we can 

 confidently affirm that, among some 400 specimens, none have occurred 

 which could possibly be mistaken for the " light."* It follows, therefore, that 

 the bulk of those which we have classed as " intermediate " can be with 

 certainty explained as blends originating from the hybridisation. 



Crosses obtained. — Cross-pairings were obtained in each generation, usually 

 in reciprocal crosses, and in not a few instances in duplicate. In many cases 

 the progeny of the crosses was also carried on down to the generation 

 collateral with that of Fi from the original cross. The complete scheme 

 upon which we intended to work may be indicated as follows : — 



Pure dark (D). — Fi to F 10 . 

 Pure light (L). — F x to Fi . 



Dark by light (called cross-pairing A). — Fi to Fio. 



Light by dark (cross-pairing a). — Fi to Fio. 



Dark by light, ex Fx (£). — F 2 to Fi . 



Light by dark, ex Fi (b). — F 2 to F w . 



Dark by light, ex F 2 (C). — F 3 to F u . 



Light by dark, ex F 2 (c). — F 3 to F 10 . 



Dark by light, ex F 3 (E). — F 4 to F 10 . 



Light by dark, ex F 3 (e). — F 4 to Fi . 



Dark by light, ex F 4 (F). — F 5 to Fi . 



Light by dark, ex F 4 (/). — F 5 to F 10 . 



Dark by light, ex F 5 (G). — F 6 to F w . 



Light by dark, ex F 5 (g). — F 6 to Fi . 



Dark by light, ex F 6 (LP). — F 7 to F i0 . 



* One curious strain is dealt with separately below, as its actual origin is altogether 

 problematical. 



