246 



The Mechanism of Evolution" in Leptinotaksa 



showing simple gametic composition. In this pair of biotype 1 blacks from 

 nature were mated and gave in F^ biotype 1, biotype 2, and biotype 6. The F^ 

 blacks when inbred gave, out of 7 pairs, 4 that came true and 3 that gave blacks 

 and type 2. In Fg and F^ the pure-breeding blacks continued to breed true and 

 the type 2 was heterozygous, giving type 2 and blacks of biotype 1, the latter 

 breeding true. Of the biotype 6, which appeared in F^, 2 pairs out of 8 gave 

 progeny, and these came true to type in Fg, F3, and F^. The biotype 2 in F^ 

 inbred gave biotype 1 and biotype 2 in Fo, but these were not mated for further 

 testing. The simple behavior of this pair shows a relatively simple gametic com- 

 position and the capacity for extracting pure-breeding biotypic races by the 

 mating of likes. 



m 





m^m 



mm ^ 



w^' m 



A"a 



^ ^ 



lE"b 



^ m 





X"a 



Ft 



■F6 



■F6 



F4 



■F8 



F2 



Fi 



■P 



Fig. 39. — Showing results obtained from a single breeding pair of L. multitmniata 

 from the Chapultepec colony of biotype 4. 



Even more simple cases have been found where blacks of biotype 1 were pure 

 homozygotes, but in nature these are not common, but may be found in almost 

 any population of emerging stock by testing enough samples. It is certain, 

 therefore, that as regards this biotype that it exists in nature in all degrees of 

 gametic constitution from pure homozygous to highly complex and intricately 

 involved heterozygous constitutions, where there are correlations with other char- 

 acters, giving extreme diversity in the progeny of a single pair. These correla- 

 tions, while of importance in the production of diversity in the pronotal char- 

 acter in the population, can not be discussed in this part of the paper. 



The conditions found in the biotype 1 pattern are equally true of any of the 

 others found in the entire population. In figure 39 are shown the results 



