PARASITOLOGY. 183 
than wide; the genital pores irregularly alternate. 
The worms may develop to a length of five feet. 
Life History.—The ripe segments detach them- 
selves and pass out to the ground with the feces ; the 
segments soon decompose and myriads of ova are 
liberated; these become disseminated by rain. The 
sheep become infested through the food and water; 
upon reaching the stomach the ovum hatches into a 
six hooked embryo which penetrates the stomach 
wall and invades the liver tissues, where it passes 
part ofits life in its transformation into the larva; later 
it leaves the liver and becomes lodged in the peri- 
toneal cavity ; here it forms a cyst which varies in size 
uptoahen’segg. This cyst is fully developed in 250 
days and is provided with two fibrous walls, an outer 
thick membrane called the hydatic membrane and 
a thin inner one called the germinal or mother mem- 
brane; from this mother membrane is developed a 
single larva which is suspended by means of a pedi- 
cle and floats in a colorless fluid; the larva consists 
of the head and neck, from which is developed the 
adult worm, when ingested by the dug. The larva 
can be seen as a small white body through the cyst 
wall; these cysts are attached to the mesentery, 
omenta or capsule of the liver. They are called 
cysticercus tenuicollis. When this cyst is devour- 
ed by the dog, the larva is liberated through the di- 
gestion of the cyst walls; upon passing out to the 
small intestines it becomes attached by means of its 
fixation apparatus, which consists of four sucker 
discs and a rostellum of hooklets, and develops into 
the adult worm in four months. 
Animals Intested.—Adult infests dog ; larva infests 
sheep ; also observed in hog and other animals. 
Parts Intested.— Adults are found in the small in- 
