272 The Mechanism of Evolution in Leptinotaesa 



tion in the population occurred in the early portion of the season, when the 

 rainfall was low but well distributed, with uncommonly widely ranging humid- 

 ity percentages and consequent desiccation during the reproduction of the 

 population that had emerged from hibernation from the previous year. 



,96-t^ ^i^?» 77-ife 



85 -\ 

 127— ^• 

 92— 



I ! '92-1-; 



( / 86— t^ 



-iS* 



:109-^.-^ 

 114_ — _^-;:; 



75 ;_^. 



10 ^r-m-'' . J^i 92 1^ V^'^'. ^- — 77 



60 '-^ ■ ^ m-- n 65 --^rr-m :\ ^^— ,r— 100 



92_-^_.,..::-:-|^,^^: ^i* 86—^:-^---%^ ^-,?— "219 



im-m^^^ ^..: 219- ^.^.^ ^--- 155 



f 7 'Im. ^- 141 / / /■■~'^^::^ 32 



/ / / \ \ / / / 



21 Tl -101 4 18 }9 71 92 18 



1705 Males. Total 3349. 1644 Females. 



Fig 54. — Census of first annual generation of 1904 at the Chapultepec colony, 

 Bhowing actual pattern conditions In population and number of Individuals In total 

 population showing the pattern observed. 



■41-^\ 11 4 17 ? 



^^' i ,-Mv^ 1— 4i^x ! I / ^^-^ 



41— ^-«» 



mi 



31 WB-k 59 T— «^ ^ £l 31 



14 -^^:^a ,17 :-—*»- : -,j^:^- 64 



87 -V#\ :im 31' 14 ----«* mr- 77 



74 ^ i^ 79 74 .- — -*W» ■«*"^ 141 



1^ V, -iM* «¥ii 186 -^ «¥t— --: 211 



' ?^,, *^ 92 / ^^ *^--- 41 



i|W|^? 8 



/ / \ m 



! /ms-K / \\- 



8 31 3 141 *^* ^ 46 13 91 



906 Males. Total 1970. 1064 Females. 



Fig 55 — Census of second annual generation at the Chapultepec colany in 1004, 

 showing pattern conditions In the pronotum and the fact that sharp dlfterencea 

 in the population may arise between successive generations. 



The second generation showed in the census essentially the same condition as 

 in the first for this year. The same groups were present, in about the same 

 strength, but in this generation there were no isolated portions of the popula- 

 tion. Biotypes 11 and 12 seem to have been lacking, and in their place 8 



