67 
FLIES AND THEIR ASSOCIATION WITH 
DISEASE. 
(Illustrated by the Lantern.) 
By Mr. J. H. ASHWORTH, D.Sc . 
November \2th, 1907. 
During the last few years there have been great advances 
in our knowledge of the part played by flies of various kinds 
in the transmission of disease. As the common house-fly 
was by no means guiltless they would first examine the 
anatomy and life history of this fly. Its proboscis, a complex 
instrument, is particularly adapted for sucking liquid food. 
It cannot use the proboscis for biting, though a great many 
people affirm they have been bitten by it. This erroneous 
impression is due to the presence of another fly, stomoxys, 
closely resembling the house-fly, which is provided with 
organs for piercing the skin and for sucking blood. As to 
the life history of the house-fly, it lays about 120 eggs at a 
time in the crevices of freshly deposited horse manure. Next 
day the little maggots hatch, feed and grow with great rapidity. 
In five to eight days the maggots, now about a third of an 
inch in length, become pupse, oval brownish bodies, not unlike 
a seed in appearance. Within this oval case the various 
parts of the adult fly are gradually built up, and when fully 
formed the head of the fly forces off the end of the oval case, 
the fly crawls out, the wings are stretched and soon become 
dry and ready for use, the skin of the body hardens and 
darkens in colour, and the fly is fitted for independent existence. 
The house-fly had been proved to be instrumental in spread- 
ing certain diseases. After a fly has crawled over substances 
contaminated with disease-germs it could be readily under- 
stood that some of these germs were likely to adhere to the 
