Analysis op Hetbkogeneity in the Population 



383 



colony, there was a wide range in the character of the population with no well- 

 developed isolated groups, hut in the Texcoco colony the sharp restrictions of 

 the central mass of the population and the evident propensity to produce vridely 

 and sharply isolated groups would seem to indicate for the two a different condi- 

 tion either in the population, in the medium, or both. Comparison of the condi- 

 tions in the two locations on the basis of the climatic data that I can give is not 

 satisfactory. In the latter part of the season of 1906 the conditions as regards 



876 Males. Total 1874. 998 Females. 



Fig. 74. — Census of first annual generation at Texcoco In 1907, showing sudden 

 marked extension of i>ronotal pattern In the array In all directions. 



8- 

 19- 



21 



-g 



369 Females. 



Fig. 75. — Census of second annual generation at Texcoco in 1907, showing 

 reduction of the general mass of the population as far as pronotal pattern la 

 concerned and Increased number of Isolated groups. 



the precipitation and its distribution were more uniform and propitious to the 

 development of this species than common, a fact that is partly indicated on the 

 climatic record by the high rainfall in the latter portion of the season, which 

 was also well distributed. The somewhat lower temperatures in this portion 

 of the season acted perhaps to check or counteract the opportunity presented by 

 the precipitation for the population to show wider ranges than common, which it 

 did not do. 



