134 



The Mechanism of Evolution in Leptinotaksa 



This set of conditions is rigorous and serves to stimulate or to accelerate dif- 

 ferent agents and operations in the two lines. When the cross is made between 

 the pure and the suspected materials, F^ shows no trace of the signaticollis 

 conditions at any point, nor does it appear in F^ unless the same set of condi- 



L. undecimlineata. L. signaticollis. 

 Fig. 9. 



tions are applied to the breeding pairs of the two at the time of breeding ; and 

 moreover, the result is not produced unless the same complex is applied to the 

 F^. The mated pairs ready for breeding are introduced into the apparatus 

 under the conditions and allowed to remain there until the eggs are deposited,. 



