DISPERSAL OF PARASITIC EGGS 20/ 



in the other four. A possible explanation of this phenomenon 

 has already been given (p. 66). 



Nicoll concludes " that 3f. dcmestica is quite unable to ingest 

 eggs as large as those of Hynienolepis diini?iuta.'' The fly, how- 

 ever, " can suck out " the eggs of D. canbmni and carr}' them for 

 at least 43 hours in its intestine. The eggs of T. inavgiiiata 

 " are fairly readily ingested not only by Musca but also by 

 Fannia canicularisl' and may be found in the intestines of the 

 flies after an interval of nearly three days. 



The longest and most important series of experiments were 

 carried out with T. sej'vata and show " unmistakably that Miisca 

 doniestica can quite readily ingest the ova of Tcenia serrata, not 

 only from the faeces, but also from intact segments of the worm." 

 The eggs when suspended in a liquid may be ingested in enormous 

 numbers, as many as 312 having been found in one fly. "Large 

 numbers can remain in the intestine of the fly for one or two 

 days, without visible change." By feeding experiments Nicoll 

 showed that young rabbits may be infected by ova received 

 from flies, and he further demonstrated " the very important 

 fact that faeces containing tape-worm segments may continue 

 to be a source of infection, from which such food as sugar may 

 be contaminated (by flies), for as long as a fortnight." 



The body and legs as carriers of eggs. 



Nicoll also investigated the length of time during which eggs 

 may adhere to the body and legs. " On flies caught during the 

 act of feeding, or immediately afterwards, I have found numerous 

 particles of fairly large size, and in many instances the eggs of 

 parasites as large as those of Ascaris incgalocepJiala. These 

 were found chiefly on the distal segments of the legs and on 

 the proboscis. When, however, the flies were allowed to clean 

 themselves before being examined, few particles were found and 

 only occasionally were eggs observed. On examining" the spot 

 where flies had rested while cleaning themselves, eggs were 

 found quite frequently. Apparently, therefore, the eggs are 

 got rid of at the spot where the fly first alights after feeding. 

 How far flies can conve)- eggs in this way depends on the 



