268 



The Mechanism of Evolution in Leptinotaesa 



neutral biotype 7 and biotype 12 (fig. 53). Combination of biotypes 7 and 9 

 give biotypes 10 and 5 in Pj and F3 as extracted forms (fig. 53). This is not 

 the place for an extensive analysis of the gametic constitution and of heredity 

 behavior, and only enough has been presented to show how exactly these " vari- 

 ation " phenomena are a product of gametic constitution, and to show how differ- 

 ing determiners are capable of rearrangement, of extensive manipulation, and 

 are able to transmute one biotype into another by altering, through its presence, 

 the configuration of the pattern complex of the pronotum. The biotypes are 

 realities, capable of independent stable existence; the determiners are no less 

 real, even though unseen, and known only through their action. Not one deter- 

 miner but several are involved, each more or less independent and capable of 

 altered relations, of being present and acting, or of being entirely removed or 

 made inactive in the complex. 



F3- 



F2' 



Fl- 



F3- 



.^ F2 



J I 



I 



Pi- 



JL 



Biotype 8 Biotype 



A 



Biotype 7 Biotype 9 

 53 



Fio. 52. — Showing behavior of biotypes 8 and 9 when pure homozygous lines 

 are crossed. 



Fio. 53. — Showing effect produced In the crossing of biotypes 10 and 5. 



In nature there is constant and unlimited mixing of these factors and deter- 

 miners in all kinds of combinations ; but out of this complex of interacting agen- 

 cies certain definite patterns always come, so that the net result is a rather stable 

 population as far as the patterns presented in any given location. The hetero- 

 geneity presented, however, is not one of quantity nor of directions of departure, 

 but is at least analogous to the diversity found in many chemical operations 

 where nearly related compounds are easily transmuted into some other through 

 the presence or absence of something whose presence determines a different 

 configuration of the system, and whose absence permits of another and diverse 

 arrangement. In this pronotal pattern, which is a system as intricate as one can 

 wish, the presence of one or two form-determiners decides the type of the central 

 a' b' h a group. The determiner of the posterior and anterior marginal spots 

 likewise determines the resultant changes found in certain biotypes, and so on 

 through the series. 



From this point of view the variation in the complex pattern as found in 

 nature presents a very different aspect. It is no longer " variation," but 

 metathesis, and the phenomena must be viewed as purely physical in character 



