344 



The Diseases of Animals 



Fig. 53. Head and section 

 of tape-worm. 



deposits eggs which pass out with the excrement. When 

 these eggs are taken into another animal's system, 

 either in the food or the water, they hatch into a 

 minute, migratory, larval form, that bores' its way 

 through the tissues until it reaches some suitable place, 

 often in the muscle, where it becomes encysted. These 

 cysts are small, rounded, yellowish masses, containing 



the worm -like structure 

 that is often visible to 

 the naked eye. These 

 cysts, when observed in 

 the muscular tissue of 

 pork, chicken, duck, etc., 

 are commonly called 

 "measles," and the meat is said to be "measly" (page 351). 

 In fish, the encysted forms of worms found in the mus- 

 cular tissue are commonly called "grubs," or "worms." 

 The cycle of the round -worms found in the intes- 

 tines is as follows : The egg deposited by the adult 

 passes out with the excrement, and gets into , the 

 food or water which may be eaten by other animals 

 In some instances, it is necessary that the egg be taken 

 in by a certain animal, in which it undergoes a larval 

 stage. In some worms, the young are brought forth 

 alive. The life-history of the fringed tape- worm (Tcenia 

 marginata) , which is frequently found infesting the 

 livers and small intestines of sheep in the middle west, 

 is unknown. 



When an animal is badly infested with intestinal 

 worms, some of the following symptoms are usually 

 shown : The coat is likely to be rough and staring, 



