Analysis of Heteeogenbitt in the Population 



285 



Compared with the Chapultepec popujation for corresponding generations, 

 this series at the Texcoeo colony show constant differences, chief of which is the 

 uniform restriction of the mass of the population to a rather narrow range in and 

 about biotype 7 j and second, the striking presence in the population of distinctly 

 isolated groups, none of which have any constancy of numbers or occurrence. 

 With the onset of environmental conditions which at other locations are opti- 



Total 1186. 574 Females. 



Fig. 76. — Census of first annual generation at Texcoeo In 1908, showing pres- 

 ence of numerous Isolated groups of considerable strengtli and an increased array 

 in the general population. 



730 Males. Total 1622. 



11 4 



792 Females. 



Fio. 77. — Census of second annual generation at Tezcoco in 1908, showing con- 

 dition in pronotal pattern. 



mum conditions in the medium, the population at Texcoeo was on the whole 

 inclined to exhibit an increased response to the conditions in the form of 

 widened ranges of the pattern combinations poresented, which may be cause and 

 effect, but not necessarily so. Commonly it would be so considered and the rela- 

 tion considered as established ; but it is in any such " establishment " assumed 

 that the material is uniform at the two locations, which may or may not be true. 

 If the populations were uniform, then the certainty of such determinations 



