18 THE HOUSE FLY—DISEASE CARRIER 
The Egg 
The eggs are minute and glistening white, and they 
are all long ovoid in shape. In length they vary from 
one-sixth of an inch to a little longer. They are laid 
in clusters of small size and irregular shape, either on 
their ends or on their sides. Seen under a high power of 
the microscope, the polished surface appears to be cov¬ 
ered with minute hexagonal markings such as is seen 
in what the histologist calls pavement epithelium. Each 
female fly lays on the average 120 eggs, or perhaps 
more, at a time and may lay several times. Forbes’s 
assistants in Illinois found that eggs from a single fly 
vary from 120 to 150 in each deposit and that as many 
as four deposits may be made, or say, 600 eggs by a 
single fly (in lit.). One hundred and twenty was the 
number observed by the writer to be the average num¬ 
ber, but Doctor Hewitt has counted as many as 150. 
The duration of the egg stage, as observed in Wash¬ 
ington, was usually eight hours; that is to say, eight 
hours after it was laid the egg hatched. These ob¬ 
servations were made in midsummer and have not been 
repeated at other times of the year. Mr. Newstead in 
Liverpool found that the eggs hatched in periods vary¬ 
ing from eight hours to three or four days, the average 
time being about twelve hours. But he noted that when 
laid in fermenting materials the incubation period was 
reduced to a minimum of eight to twelve hours. In 
a temperature of from 75 0 F. to 8o° F. they hatched 
in from eight to twelve hours; in a temperature of 6o° 
