W. Nicoll 
17;') 
rapidity and after the first day numerous larvae could usually be 
obtained within 24 hours. These followed a normal course and were 
usually ensheathed within eight or nine days from the start of the 
experiment. 
It should be mentioned that fly larvae obtained entrance into the 
plate cultures of Nos. 2 and 3 (23. iv. 15), but were not again met 
with on the plates. Bottles Nos. 2, 5 and 6, however, became infected 
with fly larvae but these were immediately removed. Nos. 1, 3 and 4 
escaped contamination. This matter of fly contamination was a 
difficulty throughout the course of these experiments, but in the later 
series it was of much less frequent occurrence. As far as'could be 
judged, however, it did not appear to affect the results. 
While on this subject it may be well to, refer to the question which 
has not infrequently been discussed, as to the part played by flies in 
the spread of parasitic worms. 
This is a matter which I had the opportunity of investigating some 
years ago (Nicoll, 1911) and the conclusion arrived at was that while 
house-flies may play an important part in the spread of certain worm 
parasites, the limit of their power was determined by the size of the 
parasitic eggs. In the case of hook-worm eggs it would be a matter 
of extreme difficulty for a fly to swallow them. A few, however, might 
adhere to the legs and body and so be carried for a short distance. 
From all we know of tlie habits of flies it is almost certain that they 
would rid themselves of such a comparatively large encumbrance as 
a hook-worm egg before proceeding very far. 
Again it has been suggested that the fly maggots might spread the 
eggs of worm parasites by passing them on to the adidt fly.' This 
suggestion was based on an unpublished observation of Stiles in the 
case of Ascaris lumbricoides. My personal experience has entirely 
failed to support the correctness of this observation. It must be 
admitted, however, that the matter has not been thoroughly investigated 
in the case of hook-worms. In none of the maggots which I have 
examined has any trace of hook-worm eggs or larvae been found. 
At the same time it must be remembered that house-flies can and do 
serve as natural intermediate hosts of worm parasites, for Ransom 
(1913) has shown that Habronentu muscae, a nematode worm which 
infects the horse; passes its early stages in the larva, pupa and adult 
of the house-fly. How the young woi'iiis find entrance into the fly 
maggots, whether by being swallowed (U' by boring their way in, is 
not made clear by Ransom, who has evidently not been able to elucidate 
