PART IV. CARRIAGE BY HOUSE-FLIES 143 



In this manner there were examined in all 229 flies, with the 

 results given in the table on page 142. 



In addition to the examination of single flies, a number of flies 

 were examined in batches, the collective droppings of each batch 

 being examined without any reference to which fly of the batch had 

 deposited the dropping. Nine batches of 6, 8, 3, 5, 3, 3, 2, 2, 4, 

 flies were examined in this way, with the result that a single 

 ankylostome egg (60 by 40 microns) was found in a dropping of 

 the first batch of flies. 



Two calliphora, two sarcophaga, and one lucilia deposited seven 

 droppings in an average of three hours and a half. Nothing was 

 found in the droppings. 



As regards the 229 flies which were examined singly, the total 

 number of droppings deposited by these was 1,470, of which 608 

 were examined. The average time each fly remained in the tube 

 before the droppings were examined was four hours and a half. * 

 The average number of droppings of each fly is between six and * 

 seven in this interval of time. In another experiment with wild 

 flies twelve were enclosed in a box made of glass slides. During the 

 first twenty-four hours after capture the flies deposited in all 283 

 droppings, given an average of 23'5 for each fly. The flies were 

 given no food after capture. 



(d) Quantity of Fteces taken up by Flies. An attempt was 

 made to obtain some indication of the quantity of faeces taken up 

 by a fly in a limited period of time. To this end a series of 

 weighing experiments were carried out in the following manner. 

 Small quantities of faeces were placed in cover-glasses, and these 

 were weighed. Two cover-glasses of approximately the same 

 weight were used in each observation. They were weighed the 

 one immediately after the other, and were then placed under two 

 glass globes, in one of which were one or more flies which had been 

 without food for two or three hours. After half an hour's exposure 

 to the flies, the cover-glass was again weighed, and the loss in 

 weight noted. The control cover-glass in the second globe without 

 flies was then weighed, and the loss in weight by evaporation 

 deducted from the loss in weight of the first cover-glass. It was 

 assumed that as the weight of cover-glass and faeces was approxi- 

 mately the same in the two cases, the loss by evaporation would be 

 the same, or nearly so. 



As a result of seven experiments in which sixty-one house-flies 

 were used the following figures representing weight in grammes 

 were obtained for the quantity of fasces taken up by a single fly : 



