312 THE SPEEAD OF INTESTINAL WORMS BY FLIES 



tape-worm segments possessed a great attraction lor flies. When 

 an intact segment of a tape-worm such as Taenia serrata, T. mar- 

 ginata or Dipylidiam caninum mixed with moderately fresh faeces 

 was presented to some flies they appeared to select the tape-wonn 

 and feed upon it in preference to the faeces. This observation was 

 repeated on several occasions. Further, when an isolated tape- 

 worm segment, some faeces and some sugar were separately intro- 

 duced into the fly cage, the flies showed a decided preference for 

 the tape-worm, which they attacked with much assiduity. This 

 preference was shown not only when the tape-worm segment was 

 fresh but even when it had lain a day or two. 



Flies, it was found, are able gradually to pierce the fairly tough 

 external covering of the tape-worm segments and to extract the 

 internal contents containing the eggs. When flies had been 

 feeding on a tape-worm segment for 5 — 10 hours their crops were 

 found greatly distended with the white milky juice of the tape- 

 worm and tape- worm eggs were found in the flies' intestines. 



Special observations were made on the feeding of the fly 

 larvae on parasitic worms. While it was found that even after 

 a lapse of three or four days, the adult _ flies were unable to 

 penetrate the thick cuticular investment of round worms such as 

 Ascaris megalocephala and Toxascaris limhata, such difficulties 

 did not exist in the case of the larvae. Fresh round worms when 

 offered to the larvae were at once attacked, but although they 

 swarmed over the worms, unless the cuticle of the worms was torn 

 or ruptured in some way, they were unable to penetrate them and 

 in the absence of other food they died. On the other hand, if the 

 round worms were cut up or broken before being given to the 

 larvae, the latter devoured the internal parts with great rapidity. 

 Commencing at one end of a broken piece they would eat their 

 way through the soft tissues leaving nothing but the cuticular 

 tube. It was found that within two or three days half a dozen 

 larvae would devour a large worm 20 or 30 times their own bulk. 

 When larvae had fed upon female egg-bearing worms large 

 numbers of eggs were found surrounding them but not actually 

 adhering to them and in the intestines of such larvae no intact 

 eggs were found, but fragments of shells were always visible. No 

 embryonic worms in any stage were found. NicoU is of the 



