344 The Diseases of Animals 
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 eneysted. These 
cysts are small, rounded, yellowish masses, containing 
the worm-like structure 
aes) that is often visible to 
soy the naked eye. These 
; (i ee EL cysts, when observed in 
: the muscular tissue of 
Fig. 53. Head and section pork, chicken, duck,etc., 
a Taal are commonly cealled 
measles,” and the meat is said to be “measly” (page 351). 
In fish, the eneysted 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 (Tenia 
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, 
