290 The Mechanism of Evolution in Leptinotaksa 



were clearly the product of the breeding of the population that had preceded, and 

 not due to introductions. These records I have shown in figures 86 and 87. 



The following year (1908), and again in 1909, the location was visited and a 

 rough census made of the conditions in the population, but with no added indi- 

 cation of change in the characters of the population of the place. The same iso- 

 lated groups occurred as in the previous years, and with frequency and in such 

 numbers that it was evident that their occurrence in the location was not entirely 

 the product of introductions, but was, in the main, the result of the response of 

 the population to the conditions of the habitat into which they were by chance 

 placed. 



31 I'^v 



46—4:-^,^ r'j^- 29 



51- — -^m m- 74 



k^ m--- 106 



fjt'^ ^-^.- 83 



/^■-■\- '^-k 41 



12 15 8 '"-■'" 



577 Males. Total 1204. 627 Females. 



Fig. 86. — Census of first annual generation at Tlalnepantla in 1907, showing 

 the pattern conditions. 



17 aiii 19 2l-T4■l^ 



ii^ 





\V.' — 



31 _V^ , ^^^---6 



38- — - ■^. 21 ^ ^":::.2l 



42 ^ ^_ ^^ 42 m m 45 



41 ^ j^ ^-i 92 31 If^ ^ 96 



'^Jf «*> 83 .^7.— 114 



/ «^ ^5* 46 '-^■^-•^' 77 



/ \ 



/ \ 0P 24 ^fe 31. 



21 8 ^^ 



583 Males. Total 1109. 526 Females. 



Fig. 87. — Census of second annual generation at Tlalnepantla in 1907, showing 

 the restriction of the mass of the population to a narrow range and the existence 

 of several distinctly separate groups in both sexes. 



The series of observation at the Tlalnepantla colony were in the character of 

 the population, as indicated by these censuses, quite different from those in the 

 other locations examined. Here as elsewhere the attempt to tie the observed 

 conditions to any portion of or to the environmental conditions as a whole is 

 argument from effect to cause or possible cause. The series may and often does 

 make a plausible array, one that strongly indicates the relation of cause and 

 effect. 



Comparison of the conditions presented in the population at the three loca- 

 tions in the valley of Mexico shows decided differences in the character of the 

 individual generations and in the sum total at each of the colonies. The 

 Chapultepec colony presents the most diversity and the greatest range. Tex- 



