32 



EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



The confluence of spots 5 and 6 is an independent variation. The speci- 

 men that Major Casey has from Sonoma County, California, and the one 

 I have from Stony Lake, Michigan, are well marked. It is very rare, with- 

 out intergrading conditions, and constitutes a distinct position of organic 

 stability. 



TABLE 8. Spots lacking in Hippodamia convergens. 

 [Percentage of beetles in which each spot is lacking.] 



The loss of the pronotal dashes (fig. 14) and the extension of the black 

 pigment on the pronotum is well marked in specimens from California 

 Strangely enough, they affect the spotless beetles most. One might 

 conclude that the result is compensatory for the lack of pigment in the 

 elytra, but in Oregon, where spotted elytra are found, the black pattern 

 of the pronotum is reduced, as shown in fig. 14, a to e. There are prob- 

 ably, therefore, two different causes for the reduction of pigment in the 

 pronota and in the elytra. The only case of an opening of the pronotal 

 dashes (fig. 14) to the margin laterad without communication cephalad 

 was at Fairfield, where the forward opening is not nearly as common as in 

 Oregon. Apparently the line of development is different in eastern Wash- 

 ington from that of western Oregon. 



TABLE 9. Combinations of spots present and absent in H. convergens from Fairfield, Wash. 



CORRELATION. 



The correlation between the confluence of spots 4 and 5 with the con- 

 fluence of spot 3 and the mark | is represented in table 10, and of 4 and 5 

 with the confluence of 1 and 3 in table 11. These tables show that the cor- 

 relation falls far short of the current notion, expressed in the systematic 

 literature, that these confluences are definitely coupled. 



An examination of table 6 shows that where black spots on the elytra 

 are absent the pronotal dashes are also absent in a large number of cases 



