75 



been killed in from nine to twelve days after feeding. In sncli cases 

 the sheep nsnally die of hemorrhage from the liver and peritonitis. This 

 is cansed by the perforations of the serous covering of the liver dae to 

 the parasites. These experiments show that the parasite is injurious to 

 sheep. The presence of a few well-advanced ci/sticerci in nearly all of 

 our sheep also shows that though the parasite may be injurious in its 

 young stages, the sheep rarely succumbs to them in their period of inva- 

 sion. After a period of about two weeks the sheep seem to have no dis- 

 comfort from them. 



Sheep may be invaded by the twnia at almost any time of the year. 

 TLe winter season, when the embryos which have been scattered by the 

 dogs become frozen, seems to be less favorable. If the dogs have 

 access to the sheei)-pens even this season will not delay the infection. 

 Lambs and yearlings appear to be most subject. Three months' lambs 

 are the youngest in which the cysticerd have been found. Experi- 

 ments in attempting to produce the cysts in old sheep by feeding gen- 

 erally'fail. Young sheep furnish the best specimens, while in five or 

 six year old sheep the cysticcrci seem to have degenerated into calca- 

 reous nodules. 



The adult twuia live in dogs. Soon after the cyst is sw^allowed the 

 tissue is digeste<l from it, and the large, watery bag, which has prob- 

 ably already lost its fluid in the mastication of the lood, disappears. 

 The head remains, and passing from the stomach into the intestine at- 

 taches itself by its hooks and cups, which serve as suckers. Here the 

 parasite, bathed in the intestinal fluids which nourish it, proceeds with 

 its development. In a day or two it lengthens and begins to show 

 cross lines, which indicate the points where the division into segments 

 is to occur. Later the segments appear and the worm gradually ma- 

 tures the organs of reproduction in them. After tenor twelve weeks 

 have passed, the i)arasite begins to lose its end segments, which have 

 fully developed embryo in them, and ore ready for the infection of sheep. 



Description. — -Twnia marginal a^ Eatsch, or Ta'nia cysticcrci tenuicoUin 

 Kiich., is the largest of the tKnia infesting dogs. It is usually, when 

 mature, about a yard long. Large specimens may be stretched, when 

 fresh, until they are 2^ yards long. The greater number of specimens 

 are, when contracted, under a yard long. The width of the worms also 

 depends on their degree of contraction, the more contracted specimens 

 being the widest. The average of relaxed specimens is about two-fifths 

 of an inch. The same specimens, when alive, might contract so much 

 as to measure three-fourths of an inch. The width of the worm gradu- 

 ally widens from its head for four-fifths of its length, and then contracts 

 slightly to the end. This species is moderately thick, measuring a little 

 over a twenty-fifth of an inch where thickest. When first taken its ap- 

 pearance is white and opaque, but when kept in water it becomes par- 

 tially transparent. It then resembles a whitened, pliable band of gela- 

 tine. At its small end is the so called head, which is separated from the 



