OBSERVATIONS ON BLOW FLIES. 193 



as the deep purple gives place to bright metallic green which is 

 the color most in evidence at the end of one and one half hours 

 after eclosion. If the fly be anaesthetized with ether the change 

 of pigment is inhibited and the deep purple color may be made 

 to persist throughout life. This does not seem in any way to 

 interfere with the normal activities of the insect. 



The assumption of the bronze color in Lucilia sericata was made 

 the subject of some investigation and it was found that the factors 

 governing the rapidity of production of this hue were to a great 

 extent of an hereditary nature. Considerable variation occurs 

 among the individuals in regard to the rapidity with which this 

 change from green to bronze occurs and in general it may be said 

 that this takes place in the males more rapidly than in the females. 

 In both sexes, however, the bronze may appear in certain regions 

 of the body before the purple has been replaced by green in other 

 parts and it would appear as if in some cases the bronze followed 

 the purple directly without the intervention of the green. Varia- 

 tion is also considerable as regards the position of the bronzing, 

 in some cases the abdomen becoming bronze while the thorax is 

 yet green, while in other cases the reverse occurs. No evidence 

 is yet found for an environmental cause influencing the rapidity 

 of bronzing, but the process appears to be altogether independent 

 of light and temperature. As regards the latter factor, however, 

 it is desirable that more thorough experiment should be performed 

 under more perfectly controlled conditions. That the chief 

 cause for bronzing, however, is hereditary appears from the 

 following experiment. 



A female of L. sericata, K)i$-E, taken near the Bussey Institu- 

 tion, March 19, 1913, produced 39 males and 43 females. Of this 

 lot those that reddened most quickly were selected and a mating 

 was obtained from one pair. This pair produced 70 males and 

 77 females. A further selection was made from the reddest of 

 these flies, which were examined in less than twenty-four hours 

 after eclosion. One of the pairs selected produced a large family 

 consisting of 366 males and 343 females. At this point the color 

 selection was abandoned, the family being continued as a selec- 

 tion for additional bristles. A rapid effect of selection was 

 noticed through the course of the experiment so that each 



