Ecological aiid Expernjiental Study of Sarcophagidce JJ 



alimentary canal. But this is evidently not a necessity, as is shown 

 by the following observations. 



In carrying on experiments it was always a matter of concern 

 from the first to guard against outside larvae. On several occasions 

 fish were covered by a screen of netting to keep out flies, but the 

 females of Sarcophaga sarraceniae invariably deposited their 

 young on the netting and these then found the fish without much 

 difficulty. While carrying on experiments indoors the flesh was 

 kept in Petri dishes and covered with like dishes. Several times 

 it happened that a female of Sarcophaga sarraceniae gained en- 

 trance to the room through the door and deposited larvae on the 

 outside of the dishes. Not being able to get at the flesh the larvae 

 perished. Furthermore, in such cases where the head of the fish 

 was hooded with cloth, the females of Lucilia caesar deposited 

 eggs very freely on the cloth and also on the loose ends of the string 

 used to tie the hood. These observations led the writer to be- 

 lieve that it is not necessarily the presence of food within the ali- 

 mentary canal that stimulates egg deposition. In this connection, 

 however, it might be interesting to note, that no eggs were secured 

 from individuals of Lucilia caesar kept under confinement with 

 plenty of accessible food. The flies crawled about on the fish 

 apparently sucking the juices, but all died in a short time. Con- 

 finement very probably was the cause. This evidently agrees 

 with experiments on the house fly cited by Howard ('oo), viz: 

 "I am inclined to believe that what may be termed the psycho- 

 logical influence of confinement, even in so large an enclosure as 

 the one used in the 1898 experiments, alarmed the flies, caused 

 their early death, and prevented them from obeying their natural 

 instincts and performing their natural functions." 



VII EXPERIMENTS UPON THE TROPISMS OF FLY LARVAE 



The following experiments and observations are not intended to 

 cover the topic of tropisms and their relation to fly larvae with any 

 degree of thoroughness. The object of this final chapter to the 

 general paper is to present a statement of experiments made on 

 movements in reaching the food and in migration, including a 

 preliminary discussion. 



