73 



When the animal is placed in a saucer of lukewarm water immedi- 

 ately after its removal from the slaughtered sheep and examined, it 

 can, by the aid of a low-power lens, be seen to possess considerable 

 peristaltic movement. This movement is produced by bundles of 

 muscles lying at right angles to each other, which may be seen appear- 

 ing as a faint striation on the surface. 



The little knob end of the bag is its essential part, and contains what 

 is to develop into the future tctnia. Sometimes the animal will extend 

 this knob into a cone, and finally thrust out of its center the very tip 

 of the cone. By careful handling this so-called head end may be 

 squeezed out by the fingers. The tip, when examined by a magnifying 

 glass, can be seen to possess four cup-like spots, with a little glittering 

 circlet of hooks between them at the very apex of the cone. 



Life history. — When these cysts have attained their hooks and cups 

 in a well developed condition, they are ready for transplanting into 

 another animal or host. The cysticercus completes its development in 

 about eight weeks. It may live a long time after this, and its cyst 

 enlarge, but the modifications it may undergo are unessential. The 

 host within which the cysts or cysticerci generally develop is the dog. 

 They may, however, also develop in other carnivora, such as the wolf 

 or coyote. 



Their emigration is a passive one. They remain encysted where they 

 are found until the sheep is slaughtered and the dogs eat the offal, or 

 until the sheep is killed by a dog or wolf and its liver is torn from its 

 place and devoured, together with any of the cysticerci which may be 

 attached. Having gotten into the intestines of the host the parasite 

 completes its development, becomes adult, and finally produces young, 

 which i)ass from the host along with the ejecta of the intestines. 



The young at this stage are egg-like. They are very small and 

 hardly visible to the naked eye. When viewed with a glass they are 

 seen to be a minute, jelly-like mass, furnished with six hooks and sur- 

 rounded by at least three membranes. The outer is thin and filled with 

 fluid ; the inner two more closely surround the embryo, and confine be- 

 tween them an oily material which serves to protect it when exposed to 

 the atmosphere. 



After passing to the ground these embryos in some way, possibly by 

 adhering to food or by floating in drinking water, make their way into 

 the sheep. When they arrive in the abomasum, or fourth stomach, it 

 is supposed that the gastric juice digests the membranes surrounding 

 the embryos and they then begin their active wandering. At this stage 

 they penetrate the walls of the fourth stomach and make their way 

 between the walls of serous membranes to the place where they finally 

 find lodgment. This active migration must often be converted into a 

 passive one after the embryo has made its way through the mucous 

 coat of the stomach, for when the embryos have been fed in large num- 

 bers to the sheep in the course of the experiments of different investi- 



