312 



The Mechanism of Evolution in Leptinotahsa 



SS41 



Fio. 119. — First census at Tlerra Blanca in 1907 showing condition in the popu- 

 lation with regard to pronotal pattern. 



29 87 

 Total 1059. 621 Females. 



Fio. 120. — Second census at Tierra Blanca in 1907, showing condition in pro- 

 notal pattern. 





11- 

 14- 



17 



97 — 



946 Males. Total 1973. 1027 Females. 



Fio. 121. — First census at Tierra Blanca in 1908, showing sudden increase in 

 certain directions in pronotal pattern and the sudden rise of three strongl7 

 developed isolated blofyplc groups in both sexes. 



38- 



41 ^g^ 4^__ 



-106 51 ^ 



-1" ^^^k- "* 



'X^Ht- 186 / ^^^^- — -^ 



/ ^, \ \ ■""" / ^ \\ 



11 14 91 58 14 17 9 85 



1231 Males. Total 2141. 910 Females. 



Fio. 122. — Second census at Tierra Blanca In 1908, showing condition in the 

 population as a whole and the persistence of isolated groups in previous censnaes. 



