276 



The Mechanism of EvoLtriioN in Leptinotaesa 



The season of 1908 was also a highly favorable one for this species at this 

 location, and therefore the results of the examinations of the population are 

 much like those of the previous year. In the first census the population shows 

 some curtailment of biotypes 5 and 6, the absence of 12, the reduction of 10 

 about equally in both sexes, so that the distribution of the sexes is essentially the 

 same. 



16 41 



12 19 4(4 

 1290 Males. 



Total 2621. 1331 Females. 



Fio. 62. — Census of first annual generation at Chapultepec colony In 1908, 

 showing about tbe same range of pattern distribution, but with fewer numbers 

 throughout and a tendency to restrict the extreme numbers, especially In biotypes 

 10, 11, and 12. 



19 J 

 41 



18 



34' 



k- 



41- 



Bl- 



'64- 



( 



36- 



4» <v 





•40 

 61 

 42 



16S 



141 



76 



12 



" ^1 ,. 

 31 -i^ . 



92- 



/ 4l / 



\ 

 14 



4 14 31 

 1083 Males. 



Total 2613. 1530 Females. 



Fio. 63. — Census of second annual generation at Chapultepec colony In 1908, 

 showing the array In the pronotal pattern of the population. 



The second census taken in this season showed much the same conditions that 

 were found in the first, with the exception that biotype 10 was present in the 

 males as an isolated group and wanting in the female population. Some minor 

 differences in the proportions of biotypes 5, 6, and 8 are shown in the array of 

 the two sexes, but are not of any significance. The conditions of the habitat 

 as shown by the meteorological records were much the same as in the previous 

 year — uniformity of distribution of the elements and lack of extreme conditions. 

 The findings for the two censuses are given in figures 62 and 63. 



