PUNCTATION OF ELYTRA. 87 



or reduction in pigmented areas, caused by changes in temperature, moisture, 

 and food supply. 



On plate 15 are given figures to show the variations observed in the mature 

 larvae of L. multitceniata, decemlincata, and signaticollis. In figs. 53 to 57 of 

 multitceniata is shown reduction of the spots and loss of many of them, and in 

 figs. 58 to 62 of decemlincata is shown the variation found in that species. 

 The two species form a rather complete series from the most spotted condition 

 (fig- 53) to the least (fig. 62). In figs. 63 to 67 of signaticollis is another 

 similar series of color variation. In all of the larvae the variations are in one 

 direction toward increase or reduction of spots. The young larvae are 

 hatched with more spots than those shown in fig. 53, and the constant 

 tendency in all of the species is to reduce the number of these areas during 

 the ontogeny of the larvae. That some succeed better than others is shown 

 in the figures on plate 17. When seriated these characters follow exactly 

 Quetelet's law for fluctuating variation. 



structural characters. 

 Individual Variation in the Pdnctation of the Elytra. 



In Leptinotarsa, Zygogramma, and Stilodes, as well as in Calligrapha, as 

 observed by Jacoby, the color markings are surrounded by deeply impressed 

 punctations, which lie above the columns of chitin and hypodermal cells con- 

 necting the two lamellae of the wing. These punctations are so correlated 

 with the color markings that they may be considered a part of the general 

 scheme of ornamentation found upon the elytra. 



The plan of the punctations found in the genus Leptinotarsa is shown in 

 dccemlineata. There are two rows of these punctations between each two 

 veins, and four in the subcostal space ; and they correspond exactly in position 

 to the edges of the stripes. Besides the stripes of punctations there are bands 

 which lie at right angles to the stripes. These bands of punctations are well 

 developed in some species, are absent in others, and appear in still other spe- 

 cies as rather infrequent variations. 



Thus there are two systems of punctation stripes and bands. The wing 

 exhibits one or the other of these, either as predominant or, more rarely, both 

 equally developed. In addition to these larger punctations there are also 

 smaller ones which are distributed without any discernible scheme of arrange- 

 ment. 



In the lineata group the punctations show much the same series of variation 

 as was found in the dark stripes already considered. There is a tendency to 

 fusion at the ends, toward reduction distally and posteriorly, and toward the 

 union of the stripes by transverse rows of punctations similar to the variations 

 found in the dark markings. Variations of the punctations in undecimlineata 



