EVOLUTION OF COLORATION. 223 



interbands. (See L. dilecta, plate 19.) Likewise on the figures on plates 

 22 and 23 it is apparent that species differentiation has followed along the 

 same lines. For example, the banded and spotted color pattern represented 

 on plate 22 shows plainly the combination of the bands with the spots. 



The immediate ancestor of these beetles is the genus Zygogramma, and 

 the next removed is Calligrapha. The color pattern on the elytron of C. 

 intermedia, which is represented on plate 22, fig. 1, is one from which all of 

 the elvtral designs in Calligrapha are easily derived by slight changes of the 

 elements thereof. Thus, a slight change consisting in the fusion of the ele- 

 ments in the central space, and the further development of the proximal, mid- 

 dle, and distal band, or of spots representing them in the ramous interspace, 

 will give the conditions found in Zygogramma clathrata, a highly variable 

 species, which is represented in two of its "variates" in figs. 2a and 2b on 

 plate 22. Likewise, by a continued development of the color centers of the 

 central space and of the transverse bands, the pattern found in another 

 variable species, Z. ornata, is easily produced. This species also shows two 

 divergent varieties figs. 3a and 3b, on plate 22. 



From the variety Z. ornata, represented in fig. 36, the elvtral patterns of 

 L. hogei (fig. 4) and dahlbomi (fig. 5) might easily be derived. Also from 

 the variety 36, by a continued increase of pigmentation, the forms L. hal- 

 dcmani (fig. 6) and its allies might easily be produced. Or the series L. 

 heydeni (fig. 7), modesta (fig. 16), and puncticollis (fig. 15), might have orig- 

 inated from the variety 30 of Z. ornata. Also the species L. lacerata (fig. 8) 

 and chalcospila (fig. 14) might be derived from the same condition by a 

 reduction of the spots and a development of the bands (lacerata) , and then by 

 the further reduction of the bands the spotted pattern of chalcospila might be 

 produced. Also from the pattern found in Z. clathrata, variation b, the pat- 

 tern of the elytron of L. stali (fig. 9) could be produced by the reduction of 

 the stripe of the central space in the region of the proximal interband ; and 

 likewise, from the variety 2a of Z. clathrata, the color pattern of L. Havo- 

 pustulata (fig. 10), belti (fig. 11), dohmi (fig. 12), and evanescens (fig. 13). 



On plate 23 are represented color patterns of another type, which, how- 

 ever, can all be derived in much the same way. If we start with a pattern 

 such as is represented in fig. 1 of Z. dulcis, which is almost the exact counter- 

 part of C. intermedia, geographica, etc., we can pass from a Calligrapha type 

 of pattern through the species of Z. malvcs, stali. aneovittata, and novem- 

 virgata to the striped Leptinotarsa elvtral pattern, simply by the fusion of 

 spots in the interspaces to form stripes, a process well represented in figs. 

 I to 5. Z. novem-virgata is an extremely variable form which shows numer- 

 ous elementary species, and from this group of elementary species the condi- 

 tions of color pattern represented on plate 23 could easily have been derived. 



It is perfectly evident that as far as the elvtral color patterns are concerned 

 the species of the genus Leptinotarsa can be arranged in a perfectly consistent 

 16 T 



