CHAPTER II. 



VARIATION IN LEPTINOTARSA. 



The characters chosen for the study of variation in these beetles are color 

 characters and structural characters. The color characters are of two kinds, 

 special and general. The special color characters are the elements and com- 

 binations of elements of the color patterns ; the general are the effects of 

 the combined color patterns in the production of melanism or albinism or 

 tendencies toward other general colors. The first have to do largely with 

 continuous or individual variability ; the second, with place and geograph- 

 ical variation. The structural characters which are considered are form, 

 size, puuctation, and glandular openings. 



Special color characters : 



(a) The color pattern on the pronotum : In the species not unicolorous, 

 as in the lineata group, the color pattern is composed of a series of bilaterally 

 symmetrical spots, designated a, I?, c, d, e, and / on the right side, and a', 

 b' , d , d', e' , and/' on the left side, and am and pm for the two median spots 

 (text-fig. i). The unicolorous prouota we shall discuss from the standpoint 

 of their intensity of color (melanism) and their development of metallicism. 



(6) The color pattern on the epicrauium : In the species not unicolorous 

 the epicrania have color centers or areas which we shall designate on the 

 right side as g, h, i, and on the left asg', h! , i' (text-fig. i). 



(c) The color pattern of the elytra : On the elytra, excepting in uni- 

 colorous species, there are stripes of color related morphologically to the 

 veins of the wing (text-fig. i), with certain others presently to be described. 

 The areas of color development parallel to the veins are the costal {cos.), 

 subcostal (s. cos.), ramous (ra.), medius {med.) , cubitus {cub.), and anal 

 {an. ). At a right angle to the veins at the base of the wing is an area of 

 color development, the basal, or first band {bas.)\ a corresponding area at 

 the apical portion of the wing, the marginal, or fifth band {mar.), and 

 between these three areas, also at right angles to the veins, the proximal, 

 or second band {prox.), the middle, or third band (?.), and the distal, or 

 fourth band {dist.) (text-fig. 3). It will be shown in the third chapter 

 that these color areas (fig. 3) are related to structures, and are invariable in 

 position excepting as the structures vary. 



{d) The color pattern of the ventral abdominal surface : In the lineata 

 group only is there a color pattern on the ventral surface. The elements of 



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