48 Mr. W. B. Alexander. Experiments on the [Jan. 3, 



Both Parents Unspeckled (Broods 14 and 39). — Offspring, 4 unspeckled, 

 1 speckled. The one speckled moth resulting from this type of mating in 

 Brood 39 is the only serious difficulty in the way of accepting a normal 

 Mendelian relationship between speckled and unspeckled types. If it 

 stood entirely alone I should have to regard it as due to some sort of error, 

 though I did my utmost to guard against mistakes. But in the history of 

 Messrs. Prout and Bacot's aberrant strain already mentioned, and in some 

 of their other broods, there are definite cases of speckled forms originating 

 from two non-speckled parents. Possibly one of the parents in these 

 cases is a heterozygote indistinguishable in appearance from a recessive. 



Both Parents .Speckled.— In some broods (15, 17, 19, 20, 23, 29, 28, 30, 33, 

 34, and 40) all the offspring are speckled ; in others (8, 21, 31, 35, 37, 32, 41, 

 and 42) some of the offspring are non-speckled. 



These eight broods consist of 161 moths, of which in theory \, or 40, 

 should be non-speckled, and 121 speckled. Actually we find that 51 were 

 non-speckled and 110 speckled. 



One Parent Speckled and One Parent Non-Speckled. — In one brood (18) all 

 the offspring were speckled ; in the remainder (10, 16, and 38) some of the 

 offspring are non-speckled. These three broods consist of 62 individuals, 

 of which theoretically 31 should be speckled and 31 unspeckled. Actually 

 we find that 37 were speckled and 25 non-speckled. 



These numbers are sufficiently near those demanded by theory to give 

 considerable support to the theory that the factor which causes the wings of 

 the English form to be much speckled with black is dominant to its absence 

 in var. canteneraria. A study of the much larger numbers reared by 

 Messrs. Prout and Bacot, now in the Oxford Museum, reveals the fact that 

 though this is evidently an approximation to the truth, it is not universally 

 true. For in several of their Fi generations a few non-speckled moths 

 occur, the numbers being as follows : — 



A 58 speckled, 2 non-speckled 



C 3 „ 



c 7 „ 



h 12 „ 



H 56 „ 



G 68 „ 1 



9* 20 „ 3 



7 Fi broods, 224 „ 6 



* Several much rubbed not included. 



