154 PARASITOLOGY. 
and one-half percent of the hogs in the United States. 
Description.—The adult worm is capillary in size 
and one-twelfth inch in length; the larva is one- 
twenty-fifth inch in length; the female is ovovivipa- 
rous; the ova undergo complete development in the 
uterus and hatch in the external genital organs and 
then escape; the larvae become encysted in lemon 
shaped cysts which appear as very minute white 
specks, scarcely visible to the unaided eye; a micro- 
scopic examination is necessary to make a diagnosis. 
Lite History.— When meat containing the live 
encysted larva is eaten by animals, in from eighteen 
to twenty hours the meat surrounding the cyst and 
cyst capsule is digested; the larva thus liberated 
develops into mature form in from three to four days; 
frequently on the third day the ovary shows ova in 
process of segmentation; ovulation commences 
about the sixth or seventh day; this period lasts five 
to six weeks, during which time as many as two 
thousand embryos may be produced by each female; 
as soon as laid the embryos pass through the stomach 
or intestinal wall and migrate to various parts of the 
body; they may burrow directly through the tissues 
or they may enter the blood and be carried by the 
blood current, or the lymph vessel and be carried by 
the lymph stream; at the end of eight or ten days 
the embryo reaches a resting place and coils in a 
kind of loop, then in a figure three shape, finally in a 
coil of about one and one-half turns. As a result of 
the irritation in the elements of the surrounding tis- 
sue there is produced a cyst enclosing the embryo; 
the embryo soon arrives at the fully developed larval 
state; the cyst is usually lemon shaped, although it 
