206 COLORATION IN LEPTINOTARSA. 



as far as is known, inherited by succeeding generations, but may serve, how- 

 ever, as vahiable protection during the Hfe of the individual. 



With decemlineata, experiments have been tried with the following food 

 plants: Solanum tuberosum, rostraHim, eleagnifolium, carolinense, dulca- 

 mara, nigrum, and melongena, Lycospersium escidentum, and Physales, three 

 species. Larvae fed upon these different plants showed some modifications 

 of the subhypodermal color, but none of importance. Thus, Solanum nigrum 

 produced a redder color in the larvae and S. carolinense a light dirty wine- 

 red, but I was not able to obtain the results attributed by Riley to the influence 

 of this food, and I conclude that they were almost certainly due to tempera- 

 ture and moisture, and not to food. From S. rostratum a yellowish color was 

 obtained in the larvae, but the woody Solanums produced no changes. 



With etiolated food white and transparent larvae were obtained exactly as 

 in Lepidoptera, but such modifications are manifestly of no importance in spe- 

 cies evolution. Also, when the food supply is scanty or the nutrition of the 

 larvae is interfered with, changes in coloration result, but these are due to mal- 

 nutrition and starvation, and not to the direct influence of any specific food. 



BXPERIMKNTS WITH SoiI^S. 



The direct influence of soils upon animals is exerted in three general ways : 

 First, by supplying the inorganic salts needed in the formation of protecting 

 or supporting tissues ; second, by a continued production of proper conditions 

 of moisture for hibernation or development in the ground ; and third, by the 

 control and modification of temperature. 



The first of these influences may be discarded, as in Leptinotarsa no salts 

 are used in the production of protective or supporting tissues. The second 

 and third, however, are of great importance, not because of the chemical com- 

 position of the soil, but because of its control of humidity and temperature, 

 and, through them, of coloration ; for all species of this genus pupate in the 

 ground, and are, therefore, subjected to the alterations in temperature and 

 humidity which soils induce. 



The modifying effects of soil are especially important in ecological studies, 

 and these will be considered in a subsequent paper. These influences are ex- 

 erted largely through the contained water — that is, a dry soil becomes intensely 

 hot by day and cools to a low degree at night by radiation, while a soil con- 

 taining much water warms slowly by day and cools slowly at night, owing to 

 the great amount of heat which water is capable of absorbing, and the reluc- 

 tance with which it is given up. The water content of soil is controlled, not 

 by abundant rainfall, nor by telluric water, but almost wholly by adhesion and 

 capillarity in the soil — that is, physical conditions alone, such as permeability, 

 capillarity, and the power to absorb and to retain water are the factors which 

 influence the moisture content of soil, and hence the coloration of these 



