294 



The Mechanism of Evolution in Leptinotarsa 



In 1906 two generations were again examined, with the results shown in 

 figures 92 and 93, no essential change being found in the population, the only- 

 item of interest being the existence of the extreme of biotype 8 present in the 



15--'-^, 



/ 

 3i 



471 Males. Total 971. 500 Females. 



Fig. 88. — Census of first iinniiiil spnorntion iit Chalclooniiila in 1004, sliowing 

 condition in pronotal pattern, and the restriction tliereof to a very narrow range. 



46 -tmi J«(0« 



-41 

 --92 

 -186 

 -92 



524 Males. Total 1025. 501 Females. 



Fig. 89. — Census of second annual generation at Chalcicomula in 1904, showing 

 further reduction in the range of pronotal pattern. 



14-^ 

 39-- 

 27-- 

 35- 



ih , , ^ 19 



yv!. <v*. 38 



^^ ff0 ^-^ 151 



/"""f ^ ^,- 88 



■ / \ <V'' " 41 



<W V — 56 

 19 



12-— 

 31 — 

 36- — 



& 



■^ V|6i-;;i;-— 196 



/-^^. •<^Si^— --55 



\ 



12 19 



22 

 580 Males. 



Total 1009. 



14 

 429 Females. 



11 



FiQ. 90. — Census of first annual generation at Chalcicomula in 1905, showing 

 a somewhat increased array of the pattern. 



3 -- 

 19 — 





14 



-11 

 -44 



-171 



-92 



56 



-39 



42 

 496 Males. Total 1036. 540 Females. 



Fig. 91. — ^Census of second annual generation at Chalcicomula in 1905, showing 

 the stable condition of the population with reference to pronotal pattern. 



males as an isolated group. The population was small, and it is probable that 

 twice as many would have shown intergrades in this direction. 



