140 



The Mechanism of Evolution in Leptinotaesa 



trimodal condition. The numerical results attained in this cross are shown in 

 table 17, which shows a close approximation of the array in the F^ to the mono- 

 hybrid ratio of 1 : 2 : 1. 



* 1 dead. 



Continued breeding and testing of the F^ heterozygous signaticollis strain 

 gave many indications of the reactions and associations that had been formed in 

 the production of it. 



This line, when treated with the test reaction used in the cross of diversa X 

 signaticollis, showed in F^, following the test, the uniform appearance of the 

 type in which the V determiner in the elytral-pattern complex had been brought 

 into relation with the Elp determiner, the two producing a general color distri- 

 bution over the elytron. Also, there were produced types in which the V de- 

 determiner manifestly had relations, productive of the strain where the pigment 

 was linked with the Pu determiner. These two conditions have been tested out 

 and their composition determined by the test reaction used in the signatir- 

 collisX diversa cross, and from each of them the undecimlineata type can be 

 recovered by the same methods in the same ratios that were found in the first 

 example. In fact, this signaticollis race that comes out in F^ of the cross is in 

 its adult characters the duplicate of that found in signaticollis x diversa in F^, 

 in so far as reactions and principles are concerned. 



In the larval characters the stock breeds true to the yellow with the meristic- 

 spot system in the line as it arises, but it can be broken and is broken up by the 

 test reaction, giving resolution into the component character agents that went 

 into it, showing in all respects its complete heterozygous character. 



The point of essential interest in this cross under the stated conditions is the 

 production of three sorts of heterozygotes, differing in their aspect, not in com- 

 position, but in arrangement of the agents in the gametes and in the reactions 

 of them in development. Two are of especial interest in that they breed true, 

 are stable associations in reactions and in gametic associations, which can, how- 

 ever, be broken up into the orginial agent groups of which they are composed. 

 The Fi production of the three types, while in the summation is an approxima- 



