50 



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



as Broods 33 and 40, consisting of 16 and 39 individuals respectively, main- 

 tained this type with practically no variation for two generations. It is 

 impossible, however, to draw a line between this type and less speckled forms, 

 as in some broods there is a perfect gradation down to the (so-called) non- 

 speckled type. 



The original London moths differed from any of my rearing in being- 

 suffused with a brown colour, which was, however, approached by some three 

 of the most speckled individuals in my Brood 8, which were all males. 

 Among the Oxford specimens there are some of this brown colour without 

 speckling, so that it is evidently due to a factor independent of the speckling. 

 I cannot account for the lack of inheritance of this colour nor for the various 

 yellow and whitish ground-colours among my own moths. As already 

 mentioned, the descendants of Brood 2 all had a uniform yellow ground- 

 colour. Amongst the unspeckled descendants of Brood 4 the males were 

 mostly of this same yellow colour and the females invariably lighter ; the 

 same is true of the pure canteneraria from Hyeres, in which, however, only 

 occasionally are the males yellow like my Brood 2, the majority being much 

 paler. I have found it impossible to classify the speckled moths according 

 to ground-colour, as, when they are much speckled, this is difficult to 

 estimate. In general, however, the females are lighter than the males. : 



There is another respect in which these moths vary to a considerable 

 extent, and that is in size. The following table shows the numbers of moths 

 among the descendants of Brood 4, of various breadths across the wings : — 

 Millimetres. 



Numbers of 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 



Males — 1 6 29 57 66 36 8 — — — 



Females — — — 5 11 24 49 66 35 12 — 



Totals — 1 6 34 68 90 85 74 35 12 — 



It will be seen that these figures form a normal curve, which is due to the 



combination of two curves, one of males with an average of about 17'5 mm., 



and one of females with an average of about 19'5 mm. 



Now, some of the individual broods depart markedly from these averages, 



e.g. :— 



Numbers Millimetres. 



of indivi- , •- * * Average. 



duals of 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. mm. 



Brood 40 $ ... — — — — 1 4 7 2 — — — 18-4 



— — — — — — 1 7 12 4 — 20-7 

 Brood 34 c?... — 1 3 7 4 — — — — — — 15-9 



— — — 2 8 2 1 — — — — 17-2 



