240 SUBKINGDOM ARTICULATA. 



swine. Leaving the intestines by boring through the walls, 

 it lays its eggs in the muscular tissues. Portions of this 

 infected meat eaten raw in Bologna sausages or ham, may 

 transfer the eggs to be hatched in the intestines of man. 

 There they multiply, and the embryos, penetrating the walls 

 of the alimentary canal, work their way through the mus- 

 cles. The victim suffers great pain and shows symptoms like 

 those of the typhoid fever. If he can endure this migration 

 of the trichinae, they become after a time encysted, and he is 

 safe, since they cannot mature until transferred to some 

 other animal. By thoroughly cooking pork the trichina is 

 destroyed. 



ORDER PLATYELMINTHES. 



General Characteristics. The Platyelminthes (flat- 

 worms) are mostly parasitic, being found in the viscera or 

 muscles of various animals. They are without bristles and 

 the segments of the body are indistinct. 



Fig. un. Distomidae (double-mouthed). The Fluke 



has one or two suckers by which it adheres. 

 The alimentary canal divides behind the mouth, 

 and terminates in blind extremities. This 

 parasite is found in the liver of sheep and deer, 

 producing the disease called " rot." 



Cestoididae (ribbon-shaped). The Tape- 

 worm of the human system is sometimes more 

 than twenty feet long, The anterior extremity 

 is furnished with hooks and suckers for anchor- 

 ing to the intestines of its victim ; but, so far as 

 Liver Fluke. a pp ea rs, there is no mouth or digestive organs, 

 and the worm seems to derive its nourishment entirely by 

 absorption through the skin. It grows by new joints formed 

 next to the head. The older ones ripen and fall off. Each 

 of these can move, and contains a multitude of eggs, which, 

 on escaping to the outer world, it scatters far and wide. 

 The eggs are oftenest swallowed by the hog, that omnivorous 

 feeder. In its stomach they hatch, and the embryos, boring 



