EVOLUTION 363 



various types of light on the colour of the pupae of the 

 common Large White Butterfly {Pieris brassicae). When 

 caterpillars about to pupate were subject to orange and 

 red light- rays, the black and white pigment in the under- 

 lying cuticle was much reduced in amount so that the 

 pupa when revealed was predominantly green. Inheritance 

 of such induced characters was estabhshed in so far as 

 the parents had displayed them. Hence Diirken con- 

 cluded that there was definite evidence of somatic influence 

 on the germ- cells. The wing-pattern of the butterflies 

 emerging from these modified pupae showed no deviation 

 from the normal characters of the species. 



A recent noteworthy contribution to this vexed question 

 has been made by J. W. H. Harrison and F. C. Garrett 

 (1926). The darkening of the wing-patterns among 

 Lepidoptera, such as that shown by Amphidasys betularia, 

 var. doiihledayaria, is often specially noticeable in manu- 

 facturing districts, and has been attributed, in some instances, 

 to contamination of the caterpillars' food through sub- 

 stances discharged into the air in those localities. Harrison 

 and Garrett experimented with common British geometrid 

 moths in which the dark (melanic) modification has been 

 rarely obsei-\'ed, and obtained for their investigations typical 

 pale-winged strains from the south of England. Cater- 

 pillars of Selenia hilunaria (Plate XIII, B) from the eggs of 

 such moths, were divided into two sets, one fed on tvvigs of 

 uncontaminated hawthorn and the other on hawthorn twigs 

 placed in a solution of lead nitrate. All the moths of the 

 former set were normal in their wing pattern through several 

 generations, but in each of the two famiHes of caterpillars 

 fed on lead-contaminated leaves, black-winged moths 

 appeared in the third generation — in one family a single 

 male out of twenty-seven, in the other two out of thirty-one. 

 In a family of the next generation, offspring of a normal 

 pair, there were two melanic females and one male. From 

 the small numbers and gradual appearance of the dark- 

 winged insects, the investigators conclude that the blacken- 

 ing of the wings of the moths was a result of the lead salt 



