MODIFICATION OF COLOR. 177 



consequcuL melanic tendency in variations. This stimulus in both directions 

 to increased pigmentation reaches a maximum between 5 and 7 C. devia- 

 tion from the normal. Beyond these, as the temperature further deviates, 

 there is a rapid fall in melanism, first to the normal, and then to a condition 

 below normal, until a marked albinic tendency is found; and this decrease in 

 pigmentation continues until the zero point is reached, beyond which no pig- 

 ment whatever is produced. The zero point is reached much sooner, how- 

 ever, in high-temperature experiments than in the low. 



The increased pigmentation caused by a slight raising of the temperature 

 can be accounted for by the fact, which has been proven by experiment, that 

 pigmentation is due solely to the action of enzymes, and that the action of 

 these enzymes is accelerated by an increase in temperature up to a certain 

 point, and thereafter retarded. With low-temperature experiments, however, 

 the phenomenon of increased pigmentation is due to the prolongation of the 

 period during which the enzymes act. The lowered temperature inhibits the 

 developmental process, and consequently emergence from the pupa; but it 

 does not interfere to the same degree with the action of the color-forming 

 enzymes. Hence, even though the amount of enzymes produced in a low 

 temperature may be less than that produced in a temperature correspondingly 

 high, the resulting pigmentation may be approximately equal in both cases, 

 owing to the retardation of development in the lower temperature and the 

 longer continued action of the pigment-producing enzymes. 



From these seven experiments, conditions of coloration were produced in 

 the imagines which simulate those found in nature in several geographical 

 areas. This becomes evident from a comparison of the distribution of the 

 variation in these experiments with that in the tables of place variation. Thus 

 the results produced by experiments 1 and 4 are like the melanic conditions 

 found in occasional generations in the northeastern United States ; or a like 

 parallel may be found by comparing the effects of experiments 2 and 5 with 

 the place variations of the south and west, or of experiments 3 and 6 with 

 those in Arizona and New Mexico. This production in experiment of condi- 

 tions found in nature in different geographical areas is conclusive proof of the 

 statement made in regard to place and geographical variations that they are 

 due solely to the natural conditions of existence. 



Another point of interest in this connection is the fact that the variation of 

 the color pattern in experiment follows the laws found in individual variation, 

 and is in strict accordance with the observations and laws derived from the 

 study of color-pattern ontogeny. 



These experiments are similar to those conducted by Dorfmeister, Weis- 

 mann, Edwards, Merrifield, Standfuss, Fischer, and others in that larvae were 

 suddenly transported just before pupation from normal conditions in nature 

 to the conditions of the experiment. The difference between my experiments 



