loitli Report on Experiments. 
365 
Fig. 2.- Egg of 
the Cattle 
Strongijle, icith 
coiled Embryo 
inside. 
Fig. 3. — Embryo 
of Strongyle 
fromtheWind- 
yipe of a Calf. 
Length of 
an inch. 
embryos to supply the place of those that are already expelled. 
The conditions being favourable, it is no exaggeration to say 
that one female worm is capable of discharging 
several millions of embryos. When it is con- 
sidered what large numbers of full-grown worms 
sometimes infest a single animal, the number of 
young that are expelled from the lungs of a single 
victim defies all calculation. One diseased ani- 
mal may indirectly be the cause of infection of 
other animals. It is fortunate, indeed, that of 
the millions of embryos discharged, only a very 
small number of them come to perfection — that 
is, of course, relatively speaking. 
The embryo, when expelled, is still invested 
by its delicate covering {chorion), but there is no 
true egg-shell (Fig. 2). The little coiled-up 
worm is perfectly transparent, and of nearly 
uniform thickness, except at the tail end of the 
body. There is no trace of a mouth, and the 
only structures noticeable are fine molecules and 
granules. These particles are pretty uniformly 
distributed within the body. The slight move- 
ments of the embryo do not alter the oval form 
of the egg, even after it has been discharged 
from the parent Avorm. The egg itself measures 
about Q of an inch in length, and 
inch from side to side. 
The Free Embryo. — The lung-worms of cattle 
and sheep are commonly said to be viviparous. 
They were so described by Gurlt long ago. The 
statement is not, indeed, altogether incorrect; 
but it is rather misleading, inasmuch as the em- 
bryos are rarely, if ever, born without their egg- 
envelope. These parasites are, in fact, ovo- 
viviparous. 
If, shortly after death, the windpipe and prin- 
cipal air-passages of a diseased calf be laid open, 
the frothy mucus within these tubes will be seen 
to contain multitudes of embryos, part of which 
remain coiled within their chorional coverings, 
the rest being free (Fig. 3). No marked differ- 
ence, either of form or of structures, can be de- 
tected on comparing the free embryos with those 
still in the egg. It will usually be observed, 
however, that the molecules and granules have sensibly increased 
in numbers, and that they have become more crowded together 
420 of an 
