1909.] Two Races of the Moth Acidalia virgularia. 143 



(2) In generation F 4 58 were reared, all intermediate and remarkably 

 constant. Excepting the slight sexual dimorphism, the variation might be 

 said to be practically nil. Progeny not obtained. 



Brood e. — Continued to generation F 7 . F 4 consisted of 77 specimens, all 

 intermediate except, perhaps, one brownish $ , which resembles some of the 

 lightest London forms ; the other 76 exceedingly constant. In F 5 , 

 49 specimens, the variation is much greater, ranging from a few of each 

 sex quite resembling the London forms to a few whitish, though certainly 

 not pure. F 6 , 78 specimens, extremely variable, though not definitely 

 segregating ; a few very dark, several darkish, one darkened in outer area, 

 numerous intermediate, numerous light or lightish, the black dot-lines then 

 generally (not always) well expressed, some with, some without, the dark 

 central shade, 2 or 3 agreeing fully with the pure light strain. In F 7 only 

 6 moths were bred, from stock, variable from dark to light. 



Brood F. — Continued to generation F 8 . The original pairing was 

 duplicated. 



(1) F 5 , 29 specimens, singularly enough, acted differently from all the 

 other first crosses, being virtually a pure light brood, and we hoped 

 that, for once, the light $ parent had acted as a dominant. Fortunately a 

 large offspring was obtained (from stock) consisting of 150 specimens. These 

 (F 6 ) are much more variable than F 5 , but cannot be split up into light and 

 dark definitely ; roughly classified, we made 45 light (perhaps a dozen pure 

 light), 95 intermediate, 10 dark (none extremely), but the gradations are so 

 extremely slight that a re-count would be almost sure to modify the 

 figures somewhat. Two pairings were obtained : one brood of F 7 (ex 

 light J x dark $ ) yielded 7 specimens, all more or less intermediate, 

 3 more dusted than the other 4 ; the other brood (ex light cjf , with strong 

 dot-lines), 6 specimens, all rather light, but only one with the lines sharp. 

 F 8 , from a pair of the lightest specimens in the former of the last-mentioned 

 broods, again proved numerically inadecpiate, only 7 coming through ; these 

 are rather variable, 6 being on the lighter side (2 or 3 pure, the others grading 

 towards intermediate), the seventh strongly dusted (dark intermediate). 

 A.ttempts to continue the strain proved unsuccessful. 



(2) F 5 here consisted of 47 specimens, the variation not considerable, the 

 general facies being very uniform, but the colour ranging from lightish (not 

 pure) to a lightish intermediate. Offspring was not obtained. 



Brood /. — Continued to generation Fi , though then on the verge of 

 extinction. F 5 , not variable, would certainly be classed as true intermediate, 

 though rather on the light side. F 6 , 64 specimens, is much more variable, 

 two or three being pure light, several others closely approaching it, many 



