86 



ZOOLOGY 



is due to germs of microscopic organisms that live in the 

 salivary glands of some kinds of mosquitoes (Anopheles) and 

 are injected into the l)lood of its victim at the time of biting. 

 The mosquito gets the malaria germs from the blood of infected 

 persons. Another genus (Stegomyia) found in the tropics dis- 

 seminates the germs of yellow fever. Still another species 



Fig. 92. — A quiet water where mosquitoes breed. 



conveys about a minute round worm, Filaria ' hominis," allied to 

 the vinegar eel, which thrives as a parasite in the blood-vessels 

 of men living in the tropics, and causes a painful and usually 

 fatal swelling of the arms and legs. The embryos are found 

 in the surface circulation only at night, during which time man 

 is most defenceless toward the mosquito. At this time they 

 are sucked out of the blood by the mosquito and develop in 

 its alimentary tract. Later they are deposited in stagnant 



1 filuin, thread. ^ of man. 



