360 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



and anaemic. It will be seen, too, that the recurrence of the 

 chills and fevers is simultaneous with the escaping of the 

 parasites from the blood corpuscles, together with the waste 

 products of their metabolism. These waste products are 

 poisonous, and it is believed that this great amount of poison 

 poured into the blood at one time causes the regular recurring 

 crisis. 



FIG. 153. Malarial mosquito, Anopheles maculipennis, on the wall. 

 (About six times natural size.) 



We have already learned that such a process of asexual re- 

 production cannot go on indefinitely, but for a long time those 

 who were studying these parasites were at a loss to know where 

 the sexual stage took place. Many men have worked on this 

 problem but perhaps most .credit will always be given to 

 Ronald Ross, a surgeon in the English army, who, after many 

 months of continuous labor, finally demonstrated that the 



