ANIMAL PARASITES AND DEGENERATION 415 



lies until the diseased flesh containing it is eaten (without 

 being perfectly cooked), and thus it finds its way into the 

 alimentary canal and thence into the intestine of 

 man. It now continues to develop until it becomes 

 full grown. 



Many animals are infested by minute parasites belonging 

 to the Protozoa or one-celled animals. The class Sporozoa 

 of the Protozoa is composed almost exclusively of parasitic 

 species living in the blood, liver, ali^ientary canal, and 



Fig. 207. Tape worm; the head, magnified, at left; the whole worm 

 may be several yards long. (After Lenckart.) 



other organs and tissue of animals. Over seven hundred 

 and fifty kinds of these Sporozoan parasites have been de- 

 scribed. Some of them, as has already been told in Chap- 

 ter XII are parasites of the human body causing terrible 

 infectious diseases among us. 



Parasitic insects. — Among the insects many live as para- 

 sites during their immature or larval life, but as adults 



