STUDIES ON THE DURATION OF LIFE 187 



haps one fourth as large as the common house fly. It 

 has striking red eyes, a brownish body, and wings of 

 length and form varying in different strains. It lives 

 normally on the surface of decaying fruit of all sorts, 

 but because of a more or less well-marked preference for 



FIG. 46. Male and female fruit fly. (Drosophila melanog aster). (From Morgan). 



banana it is sometimes called the "banana" fly. While 

 it lives on decaying fruit surfaces its food is mainly not 

 the fruit itself, but the yeast which is always growing 

 in such places. 



The life cycle of the fly is as follows : The egg laid, by 

 the female on some fairly dry spot on the food develops 

 in about 1 day into a larva. This larva or maggot crawls 

 about and feeds in the rich medium in which it finds 

 itself for about 3 to 4 days and then forms a pupa. From 

 the pupa the winged imago or adult form emerges in 

 about 4 or 5 days. The female generally begins to lay 

 eggs within the first 24 hours after she is hatched. So 



