MODIFICATION OF COLOR. 



207 



beetles. In all soils the pores which do not contain water are filled with air in 

 which the percentage of relative humidity is controlled by the amount of water 

 in neighboring pores. Likewise the cells in which these beetles pupate are 

 filled with air, the relative humidity of which is controlled by the water in the 

 pores of the surrounding earth. 



With Lcptinotarsa I have used the following soils in experiment: (1) Gla- 

 cial clay, (2) glacial till, (3) fine-grained soil, rich in humus, (4) fine sandy 

 soil, poor in humus, and (5) coarse sandy soil. The absolute water capacity 

 of these (water remaining after the excess had been drained off) and the rel- 

 ative humidity of the cavities therein were as follows : 



Table 95. Soils used. 



Larvae of L. dcceinlineata were allowed to pupate in these soils, which were 

 frequently flooded and drained, so that the absolute water content and relative 

 humidity were kept constant. The resulting modifications expressed in the 

 sedation of their variations in the imagines are as follows : 



In this table the strong influence of the soil in modifying moisture condi- 

 tions and producing color changes is apparent. The polygons of variation 

 shift either toward albinism or melanism as the moisture content of the dif- 

 15 T 



