INTESTINAL PARASITES. 147 



T^&jvm. 



The taenia or tape-worm is distinguished, as the names imply, by its 

 ribbon like form. It is composed of numerous joints, each of which in the 

 complete state is provided with male and female generative organs. It is 

 really a collection of animals, having an alternate generative power. 

 From the head are produced the segments or joints by a process of bud- 

 ding. 



The head is provided with suckers, and in some instances with hooks, 

 by which means it firmly fixes itself to the mucous membrane of the intes- 

 tine into which it has been introduced. The segments then multiply, 

 lengthening the chain as it were, and increase in size and sexual develop- 

 ment. They remain joined together until fully matured, and then separate 

 from the colony. They generate eggs which contain the embryo or germ 

 from which other taenia are developed. If these enter the stomach of a 

 suitable animal, their envelopes become softened or ruptured and the 

 embryos are set free. In some way or other they leave the digestive canal 

 and make their way to different parts of the body, meeting with condi- 

 tions favorable to their development. Should these now be introduced 

 into the intestinal canal of another animal , they would fasten themselves to 

 the mucous membrane and again a collection or colony of tape-worms be- 

 comes developed. 



To render this method of transmission clearer by illustration, the ogg 

 from the taenia of the dog if received into the body of a sheep, there finds 

 in certain parts of the organism the conditions necessary for its develop- 

 ment and growth, and becomes what is known as the ccenurus cerebralis, 

 a parasite found in the sheep's brain, which if eaten by the dog becomes 

 the taenia found in the intestine of that animal. 



Another method of propagation is illustrative ; segments of a tape-worm 

 are passed by a dog so infested, or they make their escape from the bowels 

 and locate themselves among the hairs of the coat and deposit their eggs. 

 If the animal is unfortunate enough to be affected with lice ( Trichodectes 

 Canis ), these eggs are swallowed by them. Within the bodies of the lice 

 the eggs meet with conditions which favor the rupture of their envelopes, 

 and the embryos escape and another transformation takes place. In biting 

 the parts irritated by them the lice are often swallowed by the dog, and 

 thus the germ enters and is developed into a perfect taenia in the intestinal 

 canal which it left as an egg but a few weeks previous. Through this 

 method of transmission an animal may continually infect himself, or by 

 depositing the lice containing the embryos in the kennel, shaking them 

 from his coat into the drinking water or food, they may be introduced into 

 the bodies of other dogs, and they in turn become infected. 



