154 



The Mechanism of Evolution in Leptinotaesa 



BREEDING OF Fi HETEROZYGOTES. 



The chief point of interest in this series is the extent to which there has 

 been dissociation of the gametic systems with interchange of agents or groups 

 thereof. All of these F^ fraternities are so complex that in no single instance 

 have I had the aid and space for a complete analysis of the entire condition pre- 

 sented in one fraternity which would involve in F2 and Fg hundreds of simulr 

 taneous matings to adequately test the total complexity of the interchange of 

 agents. I have, in the main, limited my efforts to the breeding and testing of 

 types and lines that showed points of interest with regard to certain gametic 

 agents and their capacity for change in position and their action in the new 

 positions. The complication, or diversity, is due to the numerous color and 

 pattern determiners that suffer interchange in crossing and the numerous 

 possible combinations thereof. Eight pairs of character groups capable of 

 metathesis are concerned. 



WITH THE DECEMLINEATA FORM DOMINANT. 



As shown in table 19 diverse types come out in F^ with decemlineata dominant 

 in form, and of these, (a), that is decemlineata in appearance, has given some 



L. decemlineata 



Fig. 10. 



L. oblongata 



interesting results. The frequency of this type in F^ is shown in table 19, in 

 which it appears that the occurrence is highly variable, may even be absent or 

 present in the population in considerable numbers, and none that has been 

 tested breed true. In figure 10 I have shown the determinations of the form- 

 index in the two parental lines. In L. decemlineata the mode and mean of 

 the index falls upon the class value 3.600-3.649, with a normal distribution on 

 either side. In L. oblongata the mode and mean fall in or close to the class value 

 3.350-3.399, also with even distribution on both sides. There is little or no over- 

 lapping of the index-curves in these two stocks; the form-index values are 

 constant, and little trouble is encountered in separating them by inspection in 



