DISEASES OF SHEEP. 315 



TAPE WORMS. 



This class ot animal parasites are all of the greatest interest 

 to the scientific student on Account of the peculiarity of their 

 habits. They doubtless cause more ailments of all kinds, some 

 quite unsuspected as the results of the special cause, than any other 

 similar cause of diseases. The sheep is unusually exposed to this 

 class of parasites and on account of the curious life history of 

 them while passing through the sheep the sheep suffer more from 

 them than from any other cause of disease. 



TENIA MARGIN ATA. 



Tenia marginata is the name of one of the most common 

 of these parasites. This name, derived from the Latin, means in 

 plain English, the margined or bordered ribbon worm. This indi- 

 cates the figure of the mature worm, which as seen in the illus- 

 tration, is a long slender ribbon-formed thing, with a corrugated 

 border or margin. It reaches a length when mature of no less 

 than eight feet and a width of nearly half an inch. In this form 

 it inhabits the intestines of the dog. Thus at the start we find 

 that the dog or some other animal related to it, is necessary +o 

 the perfection of the life history of this creature. The illustra- 

 tion given shows the general figure of this worm in its adult stage. 

 The slender part, (a) is the head, shown enlarged at (b, b,) the 

 body increasing in size and in length of section or segments to 

 the end (d, d,) from which the segments are shed as they mature 

 (c, c and d,) filled with eggs. These segments are voided by the dog 

 or other bearer and if on the grass of a pasture, or near water, it 

 is a foregone conclusion that the sheep must some time or other, 

 in the list of chances, pick up some of these eggs, when the infec- 

 tion begins. 



In the sheep, the egg soon transforms into a young worm 

 which is enclosed in a cyst or bladder, the end of the neck of 

 which is the head of the worm. The cysts mostly inhabit the 

 liver of the sheep, but have been found in the heart, lungs, and 

 muscles. To reach these resting places the minute eggs or em- 

 bryos must penetrate the wall of the sheep's stomach, and enter 

 the minute capillary veins from which they easily pass through 

 the larger veins into the liver or other resting places, where they 

 remain until they either kill the host, or die for want of the 

 means of development. In the former case the sheep perishes of 

 the disease set up in the liver by the irritating presence of the 

 parasite, or the disease may exist in the abdomen in the form of 

 peritonitis. When the dead sheep is in the course of nature made 

 a prey to the dog, the wolf or the coyote, the cysts containing the 

 eggs are swalloAved, and at once begin their final development 

 into the mature worm. 



It is readily seen that this disease due to this parasite must 

 be deadly to the sheep, which is the common result; or the para- 

 site is no longer troublesome except so far as regards the perma- 

 nent encystment of the living or dead embryo in the muscles, 



