62 VARIATION IN LEPTINOTARSA. 



INDIVIDUAL VARIATIONS. 



OBSERVATIONS AND DATA OF CONTINUOUS VARIATIONS. 



color characters. 



Individual Variation in the Color Pattern of the Pronotum. 



Variation in the color pattern of the pronotum in the lineata group. The com- 

 position of the color pattern is shown (text-fig. i) to consist of spots of dark 

 pigment upon a lighter ground. On plate 14, figs. 1 to 12, is given a series 

 of figures of pronota in L. undccimlineata to illustrate the directions of modi- 

 fication which the color pattern undergoes. In figs. 1 to 9, inclusive, is 

 shown the most common and almost the only series of variations exhibited 

 upon the pronotum in these beetles ; i. e. , fusion or apparent fusion of the 

 color areas by the extension of the spots peripherally or in certain directions, 

 so that continuous color areas are produced. From any given condition, 

 excepting the extremes, variation proceeds in two opposite directions toward 

 reduction of the pigmented area and toward increase thereof. 



If in this series we consider fig. 6 as the modal type, then figs. 5, 4, 3. 

 2, and 1 show stages in the reduction of pigment and also where sepa- 

 ration of spots first occurs. Thus in fig. 5, d, sand d', e' become separated 

 by an area of hypodermal color, and this is broadened in figs. 4, 3, 2, and 

 1. In figs. 1 and 2 is seen the last process of reduction which occurs in 

 this species, namely, the separation of a and a' and the loss of c and d ', 

 With this reduction, however, two spots hitherto merged in a + a', am and 

 ptn, are brought into view. In figs. 3 and 4 the separation of a + b and a' -f b' 

 is shown. In the opposite direction fig. 7 shows the union of d + e -\- / 

 and d' + e 1 -\-f, and in fig. 8 a further fusion of spots, so that the formula 



am 

 for the color pattern is now d , /' + d + d' -\- b' + a' + a -f- b + d -f e + /, c, 



pm 

 while in fig. 9 this process of increase in the area of individual spots is 

 further extended. 



In this series the variations are definite in two chief directions, and other 

 lines are not common, although they do exist. These less frequent varia- 

 tions consist in irregularities in the fusion, as, for example, where we find 

 a pattern which may be represented by the formula r', /', d' -f e' , b' , 



am am 



a'+a + 6 + d+e+J, c, or c' ', d' , c' , b' + a' + a + b, d, e 4- /, c . These 



ptn pm 



irregularities are due, however, to the failure of a given spot to develop 

 symmetrically with its fellow of the other side. Spots are sometimes wholly 

 absent, most commonly/ and/', the others in this series being about alike 

 in the frequency of their failure to develop. 



