134 I The Process of Evolution 



Fig. 7.4 I Map of Oxford district showing the correlation of Cepaea 

 shell type and environment. In each histogram, the left-hand column 

 represents percent of yellow shells and the right-hand column, percent 

 of effectively banded shells. Woodlands are stippled; all colonies outside 

 of woodlands are in hedgerows or rough herbage. ( From Cain and 

 Sheppard, 1954, Genetics 39.) 



I 



