496 
ON SEWAGE AND PARASITES. 
bryos of this species in fresh water, and have kept them alive 
for a period of nearly a year and a half, at the expiration of 
which time, and during the warm weather, some few of them 
succeeded in making their escape. 
According to Davaine, and speaking generally, the eggs 
of many nematode species will readily retain their vitality 
though long exposed to dryness, but their yelk contents will 
not go on developing during this period of exposure. In the 
case of Ascaris tetraptera of the mouse, however, embryonic 
formation goes on in spite of the absence of external moisture. 
He has noticed the same thing in the oxyurides of rodents. 
Dryness does not even destroy the eggs of Ascaris lumbri- 
coides and Tricocephalus dispar. It would seem, in short, that 
the eggs of nematodes, which normally take up their residence 
in cats, dogs, and the carnivora which reside in arid regions or 
deserts, will develop embryos in ova without a trace of mois- 
ture. Davaine thinks it is not necessary that nematode em- 
bryos should pass through any intermediary bearer, and he 
believes that they are often directly transferred to the stomach 
of their “ hosts” whilst adhering in the form of an impal- 
pable dust to the coats of their bearers, whence they 
are detached by the animals' frequent habit of licking the 
fur. 
With the eggs of the Ascaris megalocephala of the horse, I 
have performed numerous experiments. I have reared the 
embryos in simple fresh water, and have found them during 
warm weather escaping before the expiration of five months. 
I have also succeeded in rearing these larvae in pond mud, 
noticing, at the same time, that after their exclusion they 
grow more or less rapidly up to a certain point, after which 
they appear to stop. The addition of horses' dung to the 
soft wet mud in one case, and of cow's dung in another, 
neither appeared to advance or retard the process of embry- 
onal formation so long as the embryos were enclosed in their 
shells. On the other hand, when I reared the embryos in 
simple horse-dung, purposely kept moist, they attained a 
decidedly higher degree of organisation than those reared in 
wet mud or water. Having watched hundreds of these par- 
ticular larvse under varying conditions, I have come to the 
conclusion that, after their escape from the egg, their activity, 
growth, and strength is most marked whilst living on those 
media which happen to be the most turbid and impure. 
One of the most desirable aims experimenters have in view 
is to get a true conception of the developmental relations of 
the little threadworm, which, I believe, infests some three 
millions of the inhabitants of this country. I have experi- 
