68 



VARIATION IN LEPTINOTARSA. 



In the preceding tables of the fusion in the pronota of the different spe- 

 cies of the lineata group it appears that the directions of fusion are the same 

 for all, but the frequency of the fusion of a given spot varies in different 

 species, and this frequency is constant for large series and might be used as 

 a specific differential. In the following comparative table of the fusions of 

 a' + a and d -f- e the difference in the percentage appears : 



Table 12. Comparative frequency of fusion of a' and a, a" and e, in the 

 s/>ecies of the lineata group. 



Species. 



L. undecimlineata . 



diversa 



signaticollis . . . . 

 multitEeniata . . , 



oblongata 



rubicunda 



intermedia 



decemlineata. . . 



juncta 



defecta 



The illustrations on plate 14 and the figures given in tables 3 to 11 show 

 conclusively that the fluctuating variations of the pronotal color pattern in 

 the lineata group do not occur promiscuously and in all directions, but in two 

 well-defined lines. Rarely abnormal conditions occur, but these are the 

 results of pathological conditions operating during pupation. Individual 

 variation is definite. 



Variation in the proportion between the areas of dark and light pigment 

 gives interesting facts along the same line. Twenty classes illustrative 

 of this color relation have been established, of which fig. 30, plate 14, rep- 

 resents one extreme, with the value of 1, and fig. 32 the other, with the 

 value of 20. Somewhere between the extremes in this series all the spe- 

 cies of the lineata group find their proper places. The distribution of the 

 classes into which each species falls can best be shown by tables. 



The proportion of light to dark color on the pronotum of these beetles 

 shows in table 13 a tendency toward melanism on the one hand and albinism 

 on the other. Thus some of the species have their mode at the darker end 

 of the series (L. diversa), while others have theirs at the lighter end. In all, 

 however, the variations of this character obey Quetelet's law of individual 

 variability. With one exception no two of the species have exactly the same 

 modal condition as regards this character, a fact clearly shown in table 14. 



