146 Messrs. Prout and Bacot. On Cross-breeding of [Jan. 8, 



interesting, as in each case both the parents were more or less extreme, the 

 cf's light and the ? 's dark; the offspring of bxc (16 specimens) varied 

 little, all being intermediate or lightish ; that of G x C (4 specimens only) 

 much more, the single <$ bred being darkish, the 3 ? 's light, weakly marked. 

 In this generation (F 7 ) the specimens of b xf (34 in number) varied little, 

 the range being from lightish-intermediate to lightish, almost reaching the 

 pure Hyeres form ; the characteristic dark border of the parent strain b (2) 

 entirely disappeared. In F 8 , 47 specimens, the variation was considerably 

 greater, ranging from pure light (about 8) to pure dark (2 or 3), the majority 

 intermediate, and the extremes not very intense. F 9 was obtained in 

 triplicate ; from a light pair (especially the $ ) sprang a brood of 34 

 (labelled bf ^ ix), hardly variable, all light or lightish ; from a somewhat 

 intermediate pair a brood of 44 (labelled b/Q ix), variable, from lightish 

 (not extreme) to dark — about 8 that might be likened to average London 

 specimens ; from stock a batch of 23 (labelled bf(^ ix), slightly variable, all 

 light or lightish except 1, which is intermediate, brown. In generation Fi 

 one brood was raised, simply labelled bf x, the note of its exact parentage 

 having unfortunately been mislaid ; it consists of 32 specimeus, nearly pure 

 light and not varying much, a few virtually of the Hyeres form, but the 

 larger number with a fairly distinct central shade. 



In generation F 8 a pairing was obtained between a $ out of brood If 

 (intermediate or darkish, weakly-marked) and a $ out of brood c (inter- 

 mediate or rather light, the central shade distinct). In generation F 9 

 a brood of 33 appeared, rather variable, from light-intermediate to dark (not 

 intense), mostly weakly lined, a few strongly freckled. Their progeny 

 (Fio, 19 specimens) are also variable, from light (3) to dark (5) ; 4 are inter- 

 mediate, fairly well scaled, the rest more or less poorly scaled, weakly-marked. 



It remains to notice a strain which must be treated as of uncertain 

 ancestry, and which originated in F 6 and has been carried on to F i0 . It was 

 believed to have sprung from pure dark ancestry, a number of hibernating 

 larvae of F 3 in that strain having fed so slowly as to be still in the larval 

 state when their nephew-brood of larvae (i.e. pure dark F 4 ) arrived, and 

 having been mingled therewith ; but in F 6 the behaviour of the strain was 

 so unprecedented that we feel forced to imagine there must have been some 

 accidental importation of hybrid or light material, inexplicable though it is, 

 considering the care that was taken. Of course, it is open to those who so 

 desire to assume that there was here a true mutation, but as the white form 

 has never been known in Britain, and inbreeding has not changed the rest 

 of our pure dark stock, we ourselves cannot regard such a view as even 

 worthy to be provisionally entertained, unless confirmation be forthcoming. 



