134 



The Mechanism of Evolution in Leptinotaksa 



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

 ferent ao-ents 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 

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

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



