ON SEWAGE AND PARASITES. 
497 
merited largely with this entozoon also, and I have tried in 
vain to rear it in a monkey. I naturally selected this animal, 
thinking that the conditions (in view of man’s asserted re- 
lationship and antecedents) might turn out to be eminently 
favorable. However, I only obtained negative results ; and 
as regards the rearing experiments, under other conditions I 
only once succeeded in producing that vermiform stage of 
embryonal development which, as is now known from Yix 
and Leuckart’s researches, succeeds that of the tadpole- 
shaped condition. I did not, in short, expose the eggs in 
water to a sufficient increase of temperature. In this con- 
nection, Leuckart remarks ( f Die Menschliehen Parasiten,’ 
Band ii, s. 326 ) — “ One only needs to expose the eggs of the 
human threadworm to the action of the sun’s rays in a moist- 
ened paper envelope, when already, after the space of five or 
six hours, the tadpole-shaped embryos become slender, elon- 
gated worms, which are not altogether unlike the sexually 
mature oxyurides in form, displaying under the warmth rather 
lively movements.” Leuckart also finds that, in cases where 
the eggs have remained for a lengthened period in the intes- 
tinal canal, the embryos are capable of developing into this 
elongated or vermiform stage whilst still in the human bearer. 
Speaking of these intra-chorional embryos, he says — ie Not 
only are these elongated embryos found in the faeces, but 
also in the mucus of the rectum above and around the 
anus.” 
To cut the matter short, Leuckart holds, in partial oppo- 
sition to Vix, that, generally speaking, or under ordinary 
circumstances, the vermiform larvae escape from their egg- 
shells when the ova have been swallowed by some new bearer. 
In other words, we take in the eggs either with food or with 
drink, or in some other way ; and it then follows that, if their 
embryonic contents have acquired the vermiform stage, the 
gastric juice, aided by the struggles of the enclosed embryo, 
will ensure the escape of the larva. For myself, I will only 
say that, for the ultimate development of the mature worm, I 
cannot yet follow Davaine and others, and so disallow the 
necessity either of an intermediary animal or vegetable bearer, 
or, failing these, the assumption of a higher larval stage, 
either in moist earth, soft mud, or open waters. The ques- 
tion is by no means settled. 
I may here add, parenthetically, as it were, that during my 
attempts to rear oxyurides in rotten apples and pears, I fell 
in with two species of Anguillula, severally belonging to the 
genera Ap/ielenc/ms and Plectus established by Dr. Bastian. 
I allude to them here merely in reference to their extraordi- 
