DISPERSAL OF PARASITIC EGGS 203 



" When the alternatives of fresh faeces, sugar and bread were 

 offered, the flies did not confine their attention to any one of 

 these articles, but made repeated excursions from one to the 

 other. 



" Some interesting observations were made in regard to flies 

 feeding on segments of tape-worms. As already mentioned, 

 such segments may be deposited along with faeces or inde- 

 pendently, and in the case of several tape-worms their eggs are 

 conveyed to the exterior in this way instead of being shed 

 singly into the gut. In the course of the present experiments 

 it was rather surprising to find that such segments possessed 

 a great attraction for flies. When an intact segment of a tape- 

 worm {TcEuia scrrata, T tenia inarginata, Dipylidiuin canimini) 

 mixed with moderately fresh faeces was presented to some flies 

 they appeared to select the tape-worm and feed upon it in 

 preference to the faeces. The observation was made on several 

 occasions. Further when an isolated tape-worm segment, some 

 faeces and some sugar, were separately introduced into the fly 

 cage, the flies showed a decided preference for the tape-worm, 

 which they attacked with much assiduity. This trait was 

 displayed not only when the tape-worm was in a fresh state, 

 but even when it had lain for a day or longer. Tape-worms 

 usually possess a faint characteristic, musty odour, but whether 

 it is this or simply the juicy nature of the body which proves 

 the attraction, it is, at present, impossible to say. 



" The action of flies feeding on tape-worms was studied in 

 close detail. Applying their proboscis to the surface of the 

 worm they suck with considerable vigour for as long as half 

 a minute on end. Having selected a spot they continue there 

 for some time. From time to time a small drop of fluid was 

 seen to be extruded from the proboscis, and this apparently 

 was used to moisten the surface of the worm. The vigorous 

 sucking efforts were kept up, with intermissions, for several 

 hours. Flies examined within two or three hours after the 

 beginning of such an experiment were found to have very little 

 fluid in their crops, which contained, however, numerous large 

 bubbles of air. Later, when the flies had been feeding on 

 the tape-worm for 5 — 10 hours their crops were found greatly 



