318 



The Mechanism of Evolution in Leptinotaesa 



population of other biotype conditions, but these I have not examined or 

 attempted to follow, the localities being too remotely separated from each other 



and the materials inferior in most respects to 

 those available to me in the tropical areas, 

 where the topography had concentrated the 

 distribution without decreasing the diversity. 

 These conditions, with good transportation in 

 the region, determined the location of most of 

 my work in this direction. 



At Chicago, between 1902 and 1907, 10 

 generations in a restricted location to the 

 south of the city were examined, 2 gen- 

 erations being missed, one in 1905 and one 

 in the early part of 1906. The condition 

 in the population of this species is shown in 

 figure 136, with the arrangement of the dif- 

 ferent biotype groups in the pattern array. 

 This species is, in part, like the condition in 

 multitceniata and in the presence of biotype 

 13 is like undecimlineata, although the pres- 

 ence of the same biotypic conditions in the 

 pattern has no necessary connection phylo- 

 genctically, the condition representing solely 

 similar arrangements in the effective forces that produce the conditions observed, 

 and is the sole result of the interaction of the effective pattern-producing agents 

 and the conditions of the medium at the time of the reactions producing the 

 patterns. 



Fig. 136. — Diagram showing bio- 

 types commonly present In L. decem- 

 lineata as observed at Chicago and 

 the biotypic groups which have been 

 isolated. 



14 



11 



19 



21---!^ \ \ 



56 -^ ' 



77-—^ ] 



29 ^^ 



31 ^ 



m 



10 -t^ 



91 



42- 

 71- 

 86- 



iij^--31 

 ^ 42 



^ 17 



Cr~^ ,• ^ 51 



^^ ^ 29 



-■mi^ ^ 77 



121 



314 



:Vyt> 211 



SjMs^ 97 



^ 31 



^ 44 



t^ 77 



^-^ 86 



^- 141 



211 



t^ 151. 



^r -77 



^h — -83 



(^ 46 



^ 51 



1256 Males. Total 2695. 1439 Females. 

 Fig. 137. — First annual generation at Chicago in 1902. 



It is not worth while describing at any length the conditions in the different 

 generations examined, the series of determinations showing a restricted range 

 in the array, with not much in the presence of isolated groups in the population, 

 although such occur, as, for example, in the census of 1903 and again in 1905. 

 These are never far separated from the general mass of the population, but are 

 the extreme members of some of the biotypes, between which and the general 

 population there are no intermediate conditions presented. The array shown 

 in the censuses that are given in figures 137 to 146 show in principle the same 

 conditions that were found in thp formpr snppipa 



