176 PROBLEMS OF GENETICS 



The female bryoniae is totally unlike the others. The ground 

 colour is a full yellow, and each nervure is thickly irrorated with 

 a brown pigment often spreading so far as to hide the ground 

 almost entirely in the forewings. The males corresponding with 

 these females are not certainly distinguishable from those of our 

 own napi. Both sexes have the green veining of the underside 

 of the hind wing fully developed, rather more than is usual in the 

 lowland races, but this is not really diagnostic of the variety. 

 The first serious difficulty arises in regard to the second brood 

 of bryoniae. It is stated that there is only one brood, 16 but I feel 

 fairly sure that a second brood is sometimes produced, and that 

 the females with a yellow ground and diminished irroration of the 

 veins, not very uncommon in the Italian Alps in July to August, 

 are generally representatives of it. Such insects would of course 

 be classed with bryoniae in collections. 



My experiments began with eggs of true bryoniae females 

 caught at about 2,500 feet early in July. These emerged in 

 August-September as intermediates with yellow ground and 

 about half as much black on the upper surface as bryoniae. 

 They are exactly like the intermediates usually found in nature 

 and in the light of later experience I regard them as natural Fi 

 forms, and I think the mothers had been fertilised by napi males, 

 though I admit that in view of the rarity of natural intermediates 

 there is a difficulty in this suggestion. Three of these females 

 were mated with males raised from thorough meridionalis 

 females, and three families were produced. Two of them 

 showed distinct evidence of segregation, some being yellow and 

 some white with various intergrades, some being no blacker than 

 meridionalis and some ranging up to a dark intermediate type. 

 Part emerged in the same autumn; and part overwintered, emerg- 

 ing as the spring meridionalis or as the peculiar type which I after- 

 wards learnt to know as the spring Fi form. The distinctions 

 were fairly sharp between the several forms. But the offspring 

 of the third female gave a series practically continuous from 



16 The fact that Weismann by heating pupae obtained only one autumn speci- 

 men seems to me to show rather that a second brood can be produced than that it 

 cannot, which is the inference usually drawn. 



