Iii one very important particular the development of the lung strongle differs 

 from that of the tapeworm and fluke worm. The eggs of strongle undergo 

 development even while in the uterus, and they are deposited in the lung tubes 

 with the embryos in them in a state of active vitality. 



While watching the moving embryos in eggs, it will be seen that many of 

 them succeed in breaking the shell in which they are enclosed, and escaping 

 into the bronchial tubes or the air cells. What becomes of them after their 

 escape is not clearly known. Hundreds of them are expelled by the animal 

 during the act of coughing, but many remain, and it is not determined whether 

 or not they become mature without passing through the organism of an inter- 

 mediate host. Although this form of development must be accepted as possible, 

 it cannot be denied that there are some facts which do not support the view ; 

 for example, while the living embryos are found abundantly in the living tissues 

 along with eggs in various stages of development, not intermediate stages 

 are met with. On the other hand, there is no doubt that an immense number 

 of eggs and embryos are constantly being expelled from the breathing organs, 

 and these, falling in the pastures, are swallowed by earthworms, in the digestive 

 organs of which they undergo changes of skin, acquire a well-defined digestive 

 system, and there also takes place a sufficient development of the sexual organs 

 to enable the observer to distinguish the sex of the young worm. 



It may be presumed that young strangles, after being retained in the digestive 

 canal of the earthworm until the sexual system is well advanced, will be ejected 

 with the ordinary excreta, or worm casts, as they are called, and be taken up 

 by the animals which are grazing on the infected pastures. This view ts 

 considerably strengthened by the fact which has recently been observed, that 

 worms taken from certain pastures at regular intervals contained embryos in 

 abundance during the summer and autumn, but not during the winter. This 

 fact, however, lost some of its significance in consequence of the further dis- 

 covery of the presence of embryos in the worms from other pastures at all 

 times of the year. 



So far as the enquiry has extended, it may for the present'be assumed that 

 strongles deposit eggs in the bronchial tubes and lung tissue ; that the embryos 

 are fully formed and often hatched in the lungs, and are expelled in the act of 

 coughing ; falling on the pasture, they are swallowed by earthworms, in which 

 they undergo certain changes, Avhich fit them for residence'in the system of the 

 mammalia. At this stage the embryo is cast out by the earthworms, and eaten 

 by grazing animals. Some of the young worms will find their way into the 

 larynx and down the trachea into the bronchial tubes. Others will most 

 probably ascend the nasal chambers, and enter the wind pipe that way. 

 Those which get into the digestive system cannot be, or at least have not been, 

 traced any further ; but if they do not remain and adapt themselves to their 

 new surroundings by such changes of form as may be necessary, they must be 

 either expelled or digested. It is quite certain that typical lung strongles are 

 not found in the digestive organs. 



SEVERAL VARIETIES of strongles are found in the lungs of cattle and sheep. 

 In the calf the most common is the Strongylus micrurus, a short-tailed strongle. 

 In the sheep the Strongylus filaria, a thread-like strongle, is more often found. 



Two nematodes are also seen in the lungs of sheep the Strongylus 



