258 



The Mechanism of Evolution- in Leptinotarsa 



In F5 there were 4 with almost totally black pronotmn, or biotype 2 form, and in 

 Fb and later such were constantly present in the selected strain. Superficial 

 examination of the culture would at once decide that biotype 4 had been changed 



F4 



F3 



F2 



Fi 



m m mm 



p- 



Fig. 43. — Graphic representation of a normal cross between a true homozygous 

 acting biotype 1 and biotype 4 in L. multitwniata. 



to biotype 2, and the single male in F^ would ordinarily be interpreted as evi- 

 dence of the modification to biotype 1. This I tested out as follows : If the 

 extreme male of F^ is a biotype 1, or even partly so, breeding would test it fully 



^ m 



m^m^^ 



»_ — , — > 



Biotype 1 



Biotype 4 

 9 



Divergent 5 

 of F7 



Fig. 44. — Graphic representation of a test between a selectively divergent 

 male of biotype 4 population, shown in figure 42, in which a divergent male was 

 crossed with an homozygous female of biotype 1 and biotype 4. The test shows 

 clearly that the divergent male was distinctly a normal biotype 4 and had not been 

 altered selectively in any respect. 



as follows : This male was first mated with a pure female type 1, and second 

 with a pure female type 4 of another strain. At the same time there were mated 

 four cultures in reciprocally mated pairs from the two test strains of biotypes 1 



