258 



The Mechanism of EvoLUTiour in Leptinotaesa 



In Fj there were 4 with ahnost totally black pronotum, or biotype 2 form, and in 

 P5 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 



^N 



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

 acting biotype 1 and biotype 4 in L. multitcBtUata. 



to biotype 2, and the single male ia 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 



F3- 



F2 



Fl 



^'m 



mmm^^ 



lis 



m 



37 



Biotype 1 



t^ 



Biotype 4 

 9 



^_^ Divergent S 

 ^^ of F7 



PiQ. 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 biotrpe 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 iu reciprocally mated pairs from the two test strains of biotypes 1 



