224 ORGANISMS ILLUSTRATING BIOLOGICAL PRINCIPLES 



infective stage. Hookworm larvae may enter the body in food or 

 drink, but the normal method of entry is by actively boring through 

 the skin of the human hand or foot. For this reason the disease is 

 called "ground itch" because of the inflamed areas caused by the 



to stomach 



egg passed, 

 in fexies 



larva ready'' 

 to infect -^ 

 human iTost 



Life cycle of the liookworm. 



r-yo 



entrance of the larvae. Once liaving effected entrance into the host, 

 the minute worms are passively carried through the blood stream to 

 the heart and thence to the lungs, where they migrate out from the 

 capillaries of the lungs and work their way through the delicate 

 walls of the air sacs into the lung cavities. They next migrate up 



