336 Prof. R. Leuckart on the Developmental 
tization, not unfrequently making portions of half an inch in 
diameter perfectly impermeable. 
The ova are deposited in segmentation and possess their shells, 
which are perforated by the embryos when their development is 
complete. There is no doubt that these embryos emigrate, as 
they are not only met with in the bronchial mucus (often tinged 
with blood), but may also be traced up into the trachea. 
Unfortunately I can say nothing as to the subsequent destiny 
of the embryos. My leading experiments with them have all 
failed. I should, however, suppose that after emigration the 
young worms penetrate into mollusca or insects*, are developed in 
them for a certain period, and then, when their bearer is acci- 
dentally taken up with food, find their way from the mouth into 
the lungs. 
At present I also think we may assume the same to be the 
case_with the Strangylus filaria of our sheep +, which in many 
seasons is so abundant as considerably to thin our flocks. This 
worm inhabits especially the bronchial ramifications of medium 
diameter, in which, according to its numbers, it sometimes pro- 
duces merely a catarrhal affection, and sometimes a state of in- 
flammation,which not unfrequently diffuses itself over a great part 
of the lung and causes death. In the frothy mucus which fills 
the bronchi and trachea innumerable embryos are found, some 
of them still enveloped in the capsules in which they were born. 
They are distinguished from the previously described forms by 
the obtuseness of their caudal extremity (the absence of the 
above mentioned point), the shortness of the cesophagus, and the 
presence of a small knot which projects outwardly in the vicinity 
of the mouth. The size is also rather larger (0°54 millim.). 
In moist earth the embryos remain alive for some time, some 
of them even for several weeks. They take no nourishment, and do 
not grow, but nevertheless undergo a change of skin in from eight 
to fourteen days; by this, however, they are scarcely perceptibly 
altered, except that the caudal extremity becomes somewhat 
sharper, and the buccal knot is reduced in size. Most of the 
embryos die during the change of skin ; and even those few which 
survive it appear to close their lives soon afterwards. An attempt 
to infect a lamb with the moulting worms failed, as also did 
the transference of the bronchial mucus abundantly thronged 
with embryos, which was effected at different times upon four 
sheep. The widely diffused supposition of the contagiousness of 
* Tn many insects, especially dung-beetles, we meet with asexual Nema- 
tode worms, which might easily belong to the developmental cycle of some 
Strongylide. 
+ Not only of the sheep, but also occasionally, as I have observed, of 
the roebuck and fallow deer. 
