INSECTS 47 



of insect. The eggs of the Anopheles mosquito are larger 

 than those of the house mosquito and are laid singly, not in 

 masses (Fig. 32). In the larva stage, likewise, the two 

 insects may be easily distinguished from the fact that the 

 " malaria wriggler," while breathing, lies horizontally just 

 beneath the surface of the water, while the other species 

 hangs downward, with only the tip of the breathing tube 

 projecting to the water level (Figs. 31 and 32). 



In Figs. 31 and 32 the characteristic position of the adults 

 of the two species is shown. While the body of the house 

 mosquito is usually parallel to the surface on which it alights, 

 that of the malaria-transmitting insect is sharply tilted away 

 from the surface. 



38. Occurrence of malaria. The story of the discovery 

 that a kind of mosquito known as the Anopheles mosquito is 

 the only means, as far as we now know, by which malaria 

 may be transmitted from one individual to another, is one of 

 the most wonderful in all the history of biology. In a guide 

 leaflet on " The Malaria Mosquito " published by the Ameri- 

 can Museum of Natural History, New York City, 1 the 

 author, B. E. Dahlgren, writes as follows : 



" It was early observed that 'malaria' was apt to be prev- 

 alent during the damp and rainy seasons, and that it oc- 

 curred principally in exactly such places as are now known 

 to furnish ideal breeding grounds for the malaria mosquito. 

 That new cases of malaria appeared at the time of year when 

 the Malaria Mosquito abounded, was also recorded long 

 before it was suspected that the insect was in any way con- 



1 Every one who visits the American Museum should study care- 

 fully the wonderful set of models that show on a big scale the 

 various stages in the life history of the mosquito. These models 

 are pictured in the bulletin referred to above, which may be ob- 

 tained from the librarian of the Museum for fifteen cents. 



