The Rot in Sheep. 
113 
communication from him in January, 1857, embryos had then 
bciiun to bo formed in eggs which had been put into water by 
him in February, 1 85G, but they did not move."* 
We have a similar experiment Avith tlie eggs of the Ascaris 
himhricoidcs of the horse, now in the process of completion. They 
have been lying in water for several months, but without any 
evidence of the development of embryos. Hereafter we may find 
occasion to give the result of this experiment, together with 
others which we have adopted to elucidate the natural history of 
some of the entozoa. 
It is diflicult to say under what circumstances the embryos of 
the future distomata will be most quickly matured, so as to escape 
from the ova. The nearer, however, all experiments to determine 
this point are made to approximate the natural order of things, 
the greater will be their value. In exposition of this subject we 
come now to the experiment previously alluded to, which was 
begun on January 17, 1853. Reflection led us to adopt the fol- 
lowing plan for keeping the ova damp onh/, while they w ere being 
freely exposed to the atmosphere — imitating in this respect their 
location on a wet pasture. Two or three layers of bibulous paper 
were floated on the top of water in an ordinary soup-plate, and 
upon these were sprinkled some ova obtained fresh from the 
biliary ducts of a rotten sheep. They were carefully examined 
day by day, and after a short time it was evident that the 
developing process was quickly going on in the interior of many 
of them. 
On the 1st of March we detected, for the first time, some of the 
ova without opercula, and a number of free nucleated cells (em- 
bryos) identical with those previously described. By the 10th 
of the month more ova had parted with their opercula, and the 
number of embryos had consequently increased. Polygastric mo- 
nads of the form previously described also made their appearance, 
and, we were inclined to think, bore a proportion to the original 
liberated embryos. It is probable, however, that they had no 
connection with eacli other. Matters thus continued throughout 
the month, and into May, but without any variation of suffi- 
cient importance for the further continuance of the experi- 
ment. By far the greater part of the ova were at this time as 
perfect in their form as when originally ulaced upon the wetted 
paper. 
All helminthologists of repute appear to agree with reference 
to the nature of the embryos yielded by the fluke-egg, but, from 
the difficulties of following the changes which subsequently occur, 
* ' Animal and Vegetable Parasites,' Translated by Dr. Lankester. London, 
1S47. 
VOL. XXIII. I 
