MODIFICATION OF COLOR. 205 



(2) The color variations employed in experiment, which are purely somatic, 

 are the direct result of a response to changed environmental conditions, in 

 terms of increased or decreased activity in pigmentation. They may change 

 as rapidly, as frequently, and in as many different directions as the conditions 

 producing them change, and they have no influence whatsoever upon the col- 

 oration of succeeding generations. 



In this whole line of experiments, conducted with the purpose of deter- 

 mining the effects of temperature and moisture upon the coloration of decem- 

 lineata, many thousands of individuals have been subjected to experiment for 

 single generations, either throughout ontogeny or during the pupal period, 

 and others for successive lineal generations. I find in all, even where the most 

 extreme stimuli have been used and great modifications of coloration have 

 been produced, that the determinate character of the variations, their order of 

 appearance, and their degree of stability follow strictly the laws of variation 

 already stated. 



Temperature and moisture, the cardinal factors of environment, do not, 

 however, as is often stated, have any specific effect upon the coloration of 

 decemlineata, but each acts simply as a stimulus to accelerate or retard the 

 physiological processes involved in the production of coloration, and whether 

 alone or in combination produce identical results. Of the two factors when 

 in combination moisture is by far the more important and the determining 

 agent in the modification of color, excepting when the other is more highly 

 abnormal, a condition not often found in nature. 



The modifications produced in experiment are purely somatic and follow 

 exactly the laws of fluctuating variation. In many experiments, however, 

 the modifications effected by experiment were exactly like those found in dif- 

 ferent geographical areas, as, for example, when in beetles from Chicago 

 there were produced conditions characteristic of those from Arizona. This 

 fact is at once important and suggestive on account of its bearing upon the 

 interpretation of the phenomena described in the section on "Place and Geo- 

 graphical Variation." Finally, in experiment 27, it is clearly demonstrated 

 that the somatic variations in color are not inherited, but that they are fluc- 

 tuating, transient, and due solely to environmental stimuli which accelerate or 

 retard color development. It is from experiments like No. 27 and those pre- 

 ceding it that the proper explanation is found of the place and geographical 

 variations of this plastic species. 



Experiments with Different Foods. 



The influence of specific foods upon animal coloration has been investigated 

 to some extent in birds and insects. Poulton has shown in Lepidoptera and I 

 in Coleoptera the part that derived plant pigments play in the coloration of 

 larvae, where they are usually found as subhypodermal colors, which are not, 



