1912.] Cross-breeding of Two Races q/'Acidalia virgularia. 49 



These figures again suggest that heterozygoses may occasionally be indis- 

 tinguishable from recessives. This, as already mentioned, would account for 

 all the anomalies met with so far. 



I have studied also the F 2 families at Oxford, grouping them also into 

 speckled and non-speckled. I find that they are : — 



A 



65 spec 



kled, 



non -speckled. 



E 



32 



12 





e 



38 



10 





C 



42 



12 



„ -(-several much rubbed. 





27 



3 



„ +a few „ 



h 



22 



12 



+ „ 



H 



33 



11 



+ „ 



F 



94 



56 



„ a few doubtful. 



9 





2 





G 



4 



o 



„ doubtful, a good deal rubbed. 



F 2 



broods, 359 



118 





These numbers appear very good, as theoretically we should expect 

 358 : 119, but it will be noticed that Broods A and F compensate for one 

 another. Brood A is definitely exceptional ; Brood F is a composite one 

 derived from a number of females ; this should, of course, make no difference 

 to the numbers, but if separated it might have been found that one female 

 produced only light offspring as A produced only dark ones. 



Taking away A and F we have 200 speckled to 62 non-speckled, where 

 expectation would be 197 speckled to 65 non-speckled — a very close 

 agreement. 



It would thus appear that speckling is an ordinary Mendelian dominant 

 to the absence of speckling, but that whilst in most cases the heterozygous 

 individuals resemble the dominant they may occasionally be indistinguishable 

 from the recessive. Perhaps it would be more accurate to say that speckling 

 is usually dominant to non-speckling, but that occasionally non-speckling is 

 dominant to speckling. 



The speckled individuals vary from moths whose wings are only slightly 

 more speckled than in var. canteneraria to moths whose other markings are 

 almost obscured by black scales. I believe that this variation is met with 

 among the specimens taken wild in England, but the dark ancestors of my 

 moths were of the most thickly speckled type found in the neighbourhood of 

 London. This type occurred at intervals among the descendants of my 

 Brood 4, and I think it is probably the homozygous speckled type, especially 



VOL. LXXXV. — B. E 



