366 
The Lung Parasites of Cattle and Sheep, 
at the centre of the body. The heads and tails of the embryos 
are almost empty and of hyaline transparency. The free em- 
bryos give an average length of of an inch ; and they are 
only a trifle below the jq^q of an inch in thickness. Whilst 
free within the bronchial mucus, the embryos are more or less 
active, warmth promoting their activity. If, now, the dis- 
section be carried further down the air-passages, the parent 
worms will be found plugging the smaller branches of the 
bronchi. 
Expulsion of Embryos from ike Host. — Under ordinary cir- 
cumstances it must be clear to the most superficial observer that 
husk-affected animals are constantly discharging the eggs and 
embryos of parasites from the mouth and nostrils. The dis- 
tressing paroxysmal cough favours such discharge. If further 
proof is wanting, it is only necessary to examine the so-called 
foam from the mouth and nostrils of the living animal, when 
the embryos will be readily detected under the microscope. It 
results from all this, that the first step in the migration-process 
consists in a transfer of the young worms to the outer world, 
passively. I mean, that the embryos do not pass on to the 
grass or into the soil of their own accord. They are driven 
out, mechanically, as products of the diseased state previously 
superinduced by their parents' presence in the lungs. 
Destiny of the Embryo after Expulsion. — All manner of vague 
conjectures as to what becomes of the expelled embryos have 
been hazarded ; but only such opinions as were founded upon 
analogy have approached the truth. The developmental pheno- 
mena in this class of entozoa are very variable, fourteen well- 
marked modifications of the process having already been de- 
scribed (O. von Linstow). Obviously, if it can be shown that, 
in any one of its free-life stages, this worm is more readily 
accessible to destroying agents than in the parasitic condition, 
a great point will be gained. The animal victim and the agri- 
culturist would alike be benefited. It is in this practical view 
of the question of development that the following facts should 
be deemed worthy of consideration. 
First Exj^er in tents. — Late in the afternoon of October 22nd, 
1875, numerous embryos were placed in finely-sifted earth in 
the hollow of a watch-glass. The mould was rich and well 
moistened with water. At the same time two other vessels were 
charged with coarse earth, into which the germs and embryos of 
a separate parasite were indiscriminately cast. On the following 
day (or twenty-two hours after) living embryos were found in the 
finely-sifted soil, but in the coarse earth nearly all had perished. 
This fatality was probably due to the circumstance that shreds 
of the maternal organs of the parent worm had been introduced 
