372 



The Mechanism oe Evolution in Leptinotaksa 



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. 



88 ^t^ 

 85- 4 



127—- 



82 -r 



34 



9 



10 



60 



92- 



! I / 





10 



19 



47 

 ■9Z 



;U 



214- 

 219' 

 141 



-461 



77-1 



•92- 



861- 



aog- 



114- 

 75-^ 

 17- 

 19 — 

 65- 



im 



- m 





4tr 

 I 



19 



61 

 — 7 

 1 

 219 



-155 



/ / /■ 

 2t 77 -l« 



4 18 

 1705 Males. 



19 71 92 

 Total 3349. 1644 Females. 



18 



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

 ■bowing actual pattern conditions in population and number of indlylduali in total 

 population sliowing the pattern obserred. 



11 



m 





19 0m 



31 'r%i . 



14 bi^^ 



87 . ^ 



74 



1^ Cs^ 



s\. 



Tpaf^l^- 



'-m'-'.-fff: 



31 



\ 



3 141 



906 Males. 



31. 



79 



186 



92 



41— 



85— 



69— 



,17^ 



14- 



74 M; 



4 IT ? 





ir-7 



W: 



•St. 



m 



— -HM 



m ^' 



P^ 64 



^/- 77 



I 141 



»W!-.^^#^M 211 



l^^ll 41 



^><£ 



^^•<im 



.6 



Total 1970. 



/ 

 46 



1064 Females. 



13 91 



Fio. 55. — Census of second annual generation at the Chapultepec colany in 1904, 

 showing pattern conditions in the pronotum and the fact that sharp differences 

 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 13 seem to have been lacking, and in their place 8 



