214 COLORATION IN LEPTINOTARSA. 



in combinations, to accelerate or retard color development, and thus to modify 

 coloration in the following ways : 



(a) Toward melanic or albinic conditions, which are the most general and 

 important in coloration. 



(b) Toward suppression or accentuation of particular color areas or 

 groups thereof. 



(c) Toward changes in the colors themselves. 



(2) The factors most potent in the modification of coloration are temper- 

 ature and moisture ; soil and altitude act indirectly through moisture and tem- 

 perature, while the influence of food, light, and other factors is very slight. 



(3) Any factor acting as a stimulus produces at once the maximum re- 

 sponse which the deviation in the factor is capable of producing, and this 

 maximum response remains constant as long as the stimulus is in force, but 

 varies as the stimulus varies, and is lost when the stimulus is removed. 



(4) Any factor which deviates either above or below the normal has the 

 effect up to a certain point of producing increased pigmentation, and beyond 

 that point of retarding it. 



(5) Variations produced by the action of environmental factors during 

 ontogeny always follow the laws of fluctuating variation. New combina- 

 tions of color characters never appear as the result of stimuli applied during 

 ontogeny, and the modifications found are all in the line of accentuation or 

 reduction of the color characters natural to the species. 



(6) The variations produced in experiment resemble in their polygons 

 of distribution and in their modal classes conditions found in nature in places 

 or in seasons in which the conditions of existence are similar to those of the 

 experiment ; and a variation found in nature is to be interpreted as the result 

 of a deviation of some factor of the environment acting as a stimulus to pro- 

 duce a modification of coloration. 



(7) The variations produced by somatic stimuli are never inherited, no 

 matter how long the stimuli be applied. They are therefore of no importance 

 in evolution. They are of importance, however, in a consideration of the 

 phenomena of place and geographical variation. 



(8) Species of high variability in nature are also highly variable in experi- 

 ment, and conversely, those which are constant in nature are the same in ex- 

 periment ; hence the observed variability of a species is a good index of the 

 presence or absence of somatic plasticity, but is not necessarily an indication 

 of its ability to produce germinal variations and become a factor in evolution. 



To these conclusions the objection might be raised that in nature the fac- 

 tors of environment act as stimuli not only after the eggs are laid that is, 

 during ontogeny but also before; that they would have the same influence 

 upon the germ plasm as upon the soma, and should, therefore, produce in the 

 germ plasm variations of permanency. In all animals, however, the soma 

 acts as a protecting or insulating layer which, during the growth and fertiliza- 



