84 



EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



MEASUREMENTS. 



I have measured, by means of the eye-piece micrometer, the degree of 

 separateness or confluence of the several spots in a lot of beetles from Fair- 

 filed, Washington. Fig. 19 gives the result in the case of spots 4 and 5. 

 The micrometer units of 0.625 mm. have been used without change to avoid 

 the introduction of errors of reduction. In order to avoid errors of com- 

 binations the original classes are used, even though it makes the polygons 

 somewhat irregular. The reader may make his own combination of classes 

 mentally. Of course, since it was necessary to measure a projection of the 

 curved surface and as the distance measured was not always at the same 

 focal distance, there are errors involved. Experimental testing, however, 

 shows that the errors are too slight to affect the significant features of the 



(a) The distance between and confluence of 

 spots 4 and 5 (in units of .625 millimeters.) 

 (6) JMules. 



(c) Females. 



(d) All individuals. 



(a) 14 13 12 11 10 9 8 7 6 5 4 3 2 1 1 2 3 4 5 (' 7 S 9 ) 11 12 13 14 15 16 



(6) 1 2 2 6 10 11 8 8402 20 1 1 :5 4 8 14 15 14 13 13 2 3 2 1 0=150 



(c) 1 4 6 9 6 13 11 8 7 6 1 2 1 3 4 5 10 10 21 13 7 7 6 1 1 0=169 



(d) 1 3 6 13 19 J7 22 19 13 7 8 33 2 5 7 9 18 31 36 27 20 20 8 4 2 2 = 324 



FIG. 19. Variation ol the distance between and confluence of spots 4 and 5 in Hippodamia 

 convergens at Fairfleld, Washington. 



polygons. A novel method has been used in the construction of the curves. 

 is the case where the spots are separated by a distance less than 0.5 

 unit or confluent to the extent of having a connecting strand less than 0.5 

 unit in thickness. Increase of distance between the two spots is plotted to 

 the left. Increase in breadth of the connecting strand pigment is plotted 

 to the right. 



It will be noticed that the sexes do not materially differ ; that the dis- 

 tance apart is more variable than the thickness of the connecting band; 

 that the polygon is bimodal; and that the transitional cases fall for the 

 most part into one or the other of the two polygons. 



