244 



The Mechanism of Evolution in Leptinotaksa 



Figure 37 shows in schematic form the results from the progeny of a single 

 pair, both of which were in aspect type 1 pronotum. A pair of wild beetles with 

 black pronota from Chapultepec ' were bred in 1905-06, and gave in F^ the array 

 sho-wTi in the diagram, with some fluctuations of each of the five types which 

 are represented. Of the five types found, examples of each were mated with 

 likes. A pair of black type 1 was mated (A), and gave in F2 equal nimibers of 

 black A' and a type 2 form A". Each of these when inbred gave in F3 : from 

 the black of A' came 100 per cent black, and this continued to breed true, while 

 from the type 2 A" came black A" and type 2 again A" a, in about equal numbers. 

 The blacks in Fg A" bred true for three generations, while the type 2 A" a split 



F7. 



F6 



F5 



F4 



Fs 



Tz 



Fi 



LA' 



I A' 



^m 



^ a^ 



««l«l«ll»«i 



A' 



A": 



I I 



wwum^^ 



A' 



A' 



A" 



^" 1 I A"ab I A"ac 



A'-'J — , — I A"a 



A' I — I A" 1 I I 



m m. 



J I - J. ^^ 



D"b D"a. D"c E'ca E"c E"cb 



^ ^ ^ E"c E"b E"a | 



Fig. 37. — Schematic results showing complex nature of a pair of L. multitwniata, 

 having a pronotum of biotype 1 and heterozygous in nature. 



into blacks A" a and type 2 again, some of which A"ac continued to breed true, 

 and some A" ah split again. In Fj of type 2 two pairs were mated and only one- 

 gave progeny, and in Fg two pairs were again mated and only one gave progeny, 

 but in F4 six pairs out of eight gave progeny from type 2 matings and two gave 

 the behavior shown in A"ac, and four that of A" ah. Two races, stable, without 

 selection were obtained from A. 



From B no pairs were mated, but from C in F^ out of three such matings one 

 bred true and gave a stable race. From D, of which I bred only one pair, two 

 types appeared in Fg, a low extreme of biotype 4 (D') and a biotype 3 {D"). 



^ In all tests of materials from nature the larvee were taken and reared, and the 

 sexes isolated at emergence, so that the females were in all cases certainly virgin. 



