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 of its 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 

 up to a hen's ^'gz- 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 dog. 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. 



Ajiimals Infested, — Adult, infests dog ; larva infests 

 sheep ; also observed in hog and other animals. 

 Parts hifested. — Adults are found in the small in- 



