169 



believe that tbe deer may have been its host at the time European 

 sheep were first intioduced. There are few facts to sustain this hypoth- 

 esis. Though it may yet be too early to form a positive CDUchision, 

 further investigation may determine the section of the workl to which 

 this parasite originally belonged and then the former host may be in- 

 dicated with tolerable accuracy. 



The life history of this parasite seems to be completely known to us 

 during its development from the immature form found in the intestinal 

 tumors to the adult stage; but there is a ijeriod from the moment 

 when the eggs escape from the intestine with the excrement to the 

 time when it is found again in the intestinal tumors that must remain 

 in obscurity. After the embryo has returned into the alimentary canal 

 it makes its way through the mucous coat of the intestine and becomes 

 encysted there. The writer has been unable to learn how it passes 

 through the mucous coat, as even on the youngest specimens no sign 

 of armature is found. The very young forms found in the cysts show 

 little differentiation beyond what they could have attained in the egg- 

 shell. They are sooi. surrounded by a cyst which seems to belong to 

 them and to have been created by them ; but whether this cyst is the 

 remains of a, molt or not can not be asserted. Later in their history 

 they become surrounded by the products of the inflammation they ex- 

 cite in the surrounding tissues, and eventually break from the cyst and 

 live in the cheesy mass of the tumor. In this stage of their growth the 

 worms exhibit the intestine and oral cup and indistinct unicellular 

 glands. They then molt, and show all these features in more distinct 

 outline. Having attained a length of from 3 to 4'"'", or less than one- 

 sixth of an inch, they break from the tumors to begin their life in the 

 intestine. In the latter they continue their growth and becoming sex- 

 ually perfect and produce eggs which eventually go through the same 

 cycle. 



In developing, this worm molts at least three times — once in passing 

 out of the stage in which it has no mouth or intestines, once during 

 the development of these parts as we find them in the embryo, and 

 once while the worm changes from the embryonic form to the adult form. 



Disease. — The harm that these parasites do the sheep is directly 

 dependent on their numbers and life history. Yearlings maj'^ show 

 considerable infection, but it is usually in older sheep that the most 

 abun<lant infection occurs. The disease is a seasonal one, in that it can 

 be found in best development in the winter. The lambs begin to be in- 

 fected in the summer and fall, and from that time the tumors formed 

 increase in size until early in the spring of the next year, when they 

 gradually grow smaller but probably do not entirely disappear. 



Pathology. — A study of the fresh tumors by compressing the smaller 

 ones between two glasses and by dissecting larger specimens gives the 

 following results: The small tumors, which are scarcely the size of a 

 pinhead, are found in the snbiuiicons tissue. They appear like a sac filled 



