i88 



COLORATION IN LEPTINOTARSA. 



their color ontogeny in successive lineal generations. Moreover, if the stim- 

 ulus be removed the coloration at once shows its ephemeral character by going 

 back to the normal condition, and does not in succeeding generations exhibit 

 any tendency to repeat the modification. Some of my material, which was 

 experimented upon along this line for from twelve to fifteen lineal genera- 

 tions, still showed no trace whatever of permanent modification even with 

 intense selection. 



I conclude, therefore, that deviations in temperature, when applied to Z<. 

 decemlineata, act simply as stimuli toward the acceleration or retardation of 

 pigmentation, and that the responses attain their maxima at once, are never 

 increased (unless the stimulus be changed), and disappear as soon as the stim- 

 uli are removed. The results in color modification are purely transient, so- 

 matic variations, which, however, may produce a strong prophetic or historic 

 skewness in the variation polygon, and may correspond very closely, as I have 

 found in many of my experiments, to those variations found to exist in nature 

 as place and geographical variations. 



Nowhere in these experiments does evidence appear which would indicate 

 that temperature has any specific effect upon the coloration of these beetles. 

 It in all cases acts simply as a stimulus toward the production of results which 

 are exactly the same as those which I have brought about by other agencies. 



MoisicuRE Experiments. 



The effects of moisture upon the production of color modification has been 

 determined by subjecting L. decemlineata to varying percentages of relative 

 humidity. Numerous experiments have been tried which I shall combine into 

 a few large experiments, as in those with temperature. 



Experiment i6. — To deiermine the effect of a moderate increase in relative humidity 

 upon the color and color pattern of L. decemlineata. 



Conditions. — Relative humidity lo per cent above the average in nature, 

 with other conditions normal. 



Apparatus. — Glass tanks arranged for the absolute control of moisture. 



In these experiments, which were conducted during the years 1898 to 1904, 

 4,500 eggs collected at random were used, from which 4,000 larvae hatched. 

 These were kept in the following conditions throughout life : 



Table 74. — Humidity conditions. 



Humidity— 



7 a. m. 



10 a. in. 



I p. tn. 



3pm- 



8 p. m. 



Maxi- 

 mum. 



Mini- 

 mum. 



Aver- 

 age. 



Deviation 



from 

 normal. 



In nature 



In experiment . 



Perct. 



*IOO 

 *IOO 



Perct. 



65 



85 



Perct. 



50 

 60 



Per ct. 



55 



75 



Per ct. 

 *IOO 

 *IOO 



Perct. 

 100 

 TOO 



Per ct. 



43 

 55 



Per ct. 



74 

 84 



Per ct. 





 + 10 



*Dew. 



