AETHROPODA 



FIG. 20. Culex, male and female. Photograph, 

 three times natural size. 



ponds and marshes. 

 Where draining is 

 impossible the larvse 

 have been killed by 

 pouring kerosene 

 over the water, which 

 prevents them from 

 getting any air. A 

 quart of the oil is 

 sufficient for an area 

 of five hundred 



square feet. It should be applied every two weeks during 

 warm weather. Cuba spent a hundred thousand dollars 

 in one year to control 

 the mosquito pest, and 

 as a result Havana was 

 freed of yellow fever for 

 the first time within a 

 hundred years. Experi- 

 ments conducted in my 

 laboratory show that 

 most ponds may be kept 

 free of mosquitoes by 

 introducing into them 

 newts, blunt-nosed sala- 

 manders, fish, or dragon- 

 fly larvse. 



The crane flies resem- 



FlG. 21. Blood corpuscles of a patient with 

 malarial fever. Two corpuscles contain the 

 parasites. Photograph, enlarged one thou- 

 sand diameters. 



ble the mosquitoes, but 



most of them are much larger and they have no 



scales on the wings, the sure mark of a mosquito. The 



