PREVENTIVE MEASURES 205 



extent. Confining ourselves strictly to the fly question 

 and to no other, an earth closet unprovided with a 

 removable bucket and from which the contents are re- 

 moved only at considerable intervals is little better than 

 the uncared-for privy, except that it is usually less ac- 

 cessible to flies. A slight covering of earth over the 

 contents is no protection against the emergence of 

 adult flies coming from larvae within the substance. 

 It is not a protection against infestation from flies 

 coming in from outside, since these have been shown 

 to lay their eggs upon the earth covering excreta. 

 When the eggs hatch, the young larvae, being very ac- 

 tive, soon burrow to their proper food. 



Accurate experiments have been made by several 

 observers concerning the distance which the newly 

 emerged fly will struggle through earth to the air. 

 Hine (in lit.) experimented with ordinary soil and 

 found in a single experiment that adults were not able 

 to emerge from a depth of six inches, but Stiles and 

 Gardner, of the U. S. Public Health and Marine-Hos- 

 pital Service, have shown that, in experiments with 

 sterilized sand, house flies to the number of thirty- 

 seven, issuing from fecal material buried in a screened 

 standpipe under forty-eight inches of sand, came to 

 the surface. Some of these flies were sent to the 

 writer's office for determination and were named by 

 Mr. Coquillett. They were in a somewhat damaged 

 condition, due probably to their long struggle for free- 

 dom. In the same series of experiments, other flies of 

 undetermined genus and species struggled up to free- 



