266 The Mechanism of EvoLUTioisr in Leptinotarsa 



One test of the action of these determiners can be made as follows : A race of 

 biotype 4, which has normally the same form-determiner as the normal melano- 

 thorax type, when crossed with the melanothorax, gives an F^ population variable 

 from dominant type 1 to dominant type 4 (fig. 49) . In F2 always there occurs 

 the one form and three pronotal types — type 4, variable intermediates, and type 

 1. The first and last are homozygous, the second heterozygous. The only 

 gametic differences contrasted are the pronotal biotypes 1 and 4. If, however, a 

 cross is made between the biotype 4 and the black pronotum plus the multilineata 

 form-factor, there results an F^ progeny variable but of biotype 4 character. In 

 F2, however, there result again three general groups in form, and each variable 

 as regards pronotal pattern. There appears a group of long, narrow forms — 

 broad, oval, rounded, and intermediates. The ratios of these are variable, but 

 appear to be present as 1 : 2 : 4 ; at least the most numerous group is always the 

 broad, oval multitcejiiata form, the least numerous are the multilineata form. It 

 is in this latter that there occurs the evidence of the action of the form-deter- 

 miner, because here occurs in all instances numerous examples of the biotypes 9, 

 10, 11, and 12, where a' h' a h series are parallel and not a broadly open V, 

 as in the other biotypes. Between the two crosses of biotype 4, the only differ- 



F2- 



m w^ m 



L- Biotype 1 Biotype 4 



Fig. 49. — a graphic representation of the action of these determiners showing 

 the appearance of pionotal pattern biotypes not present in the original stocl£. 



ence is the presence of the form-determiner, and clearly the presence of the form- 

 determiner acts to change definitely the pattern of this central system of spots 

 and their position, configuration, and interreiacions. Its presence has produced, 

 and does produce each time, this definite and exact transmutation, in individuals 

 possessing the factor, the pronotal pattern of either types 9, 10, 11, or 12, or of 

 entire black. There is in this a clear transmutation of biotypes, a transmuta- 

 tion due to a determiner for form, whose presence and action can be experiment- 

 ally proven. The process which is productive of this change is a synthesis, and 

 recombination following upon an organic metathesis produced by combining 

 unlikes in an interacting complex. This result is shown in figure 50, where bio- 

 types 9, 10, and 11 result, and could by extraction be obtained pure in F3, F^, or 



In the same way and by the same method other changes less marked in visible 

 manifestation, but none the less definite and capable of demonstration, can be 

 produced. Thus pure homozygous biotype 3 X biotype 8 will give in Fj and Fg 

 homozygous biotype 6 individuals, from which a de novo strain of biotype 6 can 

 be obtained. Biotype 8, like biotype 7, is a neutral one with fusions not estab- 

 lished and lacking the marginal areas. Biotype 3 carries the marginal centers 

 and the interaction of 8 x 3 gives a transverse system of combinations, as shown 



