156 



The Mechanism of Evolution in Leptinotarsa 



test I have used only pure white, biotype 10 lines of oblongata. Y^ in the test 

 shows an array that is suggestive only of a monohybrid reaction, the oblongata, 

 the tested type, and an intermediate coming out in nearly perfect ratios (table 

 20) showing that the types in the test have acted as imits, neither gametic 

 system having been broken or interchanged agents. This test is of interest in 

 that it shows that the race does not have in it the characters of oblongata in at 

 least easily available form, else there would have appeared in F^ of this com- 

 bination, or at least in F^, some indication of them. As a test reaction this is 

 only suggestive, not in any way final. 



When crossed with the decemlineata parent stock, the product in F^ is an 

 intermediate array, and in Fo there appear the three types of form-index values, 

 as shown in figure 11. The reaction seems to have been of the simplest type 

 possible, in that the two gametic systems acted as units and suffered no change 

 in the passage through the F^ hybrids. 



Table 20. 



Pair A, F„ 



Pair B, F., 



Pair C, F, 



PairD, Fo... 



Pair E, F„ 



Pair F, F„ 



Observed 



Expected on basis of monohy 

 brid reaction. 



Decemlineata 

 type. 



20 

 37 

 12 

 13 

 20 

 16 



118 

 117 



Intermediate 

 type. 



47 

 74 

 3 

 15 

 61 

 33 



233 



234 



Oblongata 

 type. 



19 

 36 

 9 

 11 

 27 

 15 



117 

 117 



Total. 



86 

 147 



24 



39 

 108 



64 



468 

 468 



A more conclusive test was made by crossing the type with a line of L. multi- 

 tceniata biotype melanothorax, that was known to be pure for form-determiner 

 of a value of 1.1950, and with only the pronotal pattern of melanothorax present. 

 This combination showed dominance of the melanotliorax type in Fj, but in Fg 

 there appeared a complicated array that gives indication of the nature of the 

 special race investigated. This I have shown in schematic form in plate 17. 



The array given in plate 17 does not show the entire complexity of the Fg 

 product, which is further complicated by juvenile stages and groupings of 

 adult characters, but shows the essential adult conditions that are present in 

 Fo, indicating what the suspected race was composed of. An interchange of the 

 characters takes place, such that the Fg shows new combinations and types not 

 present in the original lines. Most striking is the occurrence in F2 of a biotype 

 7 multitceniata type that is the product of a synthetic combination between the 

 pattern system of the pronotum of the tested type and the melanothorax stock, in 

 which the pronotal pattern systems have been interchanged, giving as a result the 

 type shown in Fg of plate 17 (A). The pattern type of the tested line is that of 

 oblongata, in which there are present all of the elements that occur in multi- 

 tceniata, but in different relation. There also is obtained the decemlineata type 

 (B), the tested type (C), melanothorax type (F), tested type with melano- 



