88 



PRACTICAL ZOOLOGY 



fever is the commonest; it is caused by a Protozoon named 

 Plasmodium vivax and causes " chills and fever " every third 

 day. (2) Quartan fever is due to Plasmodium malarice; it 

 causes " chills and fever " every fourth day. (3) Pernicious, 

 tropical, or aestivo-autumnal fever is caused by Plasmodium 

 falciparum and produces " chills and fever " at irregular inter- 

 vals. Not all mosquitoes carry these germs, only those belong- 

 ing to a group with the scientific name Anopheles. Fortunately 

 Culex mosquitoes are more common than Anopheles mosquitoes 



FIG. 55. Pupa of house mosquito FIG. 56. Pupa of malaria mosquito at sur- 

 at surface of water. face of water. (After Howard.) 



and are comparatively harmless. The two kinds can be dis- 

 tinguished by the position of the body when at rest; Anopheles 

 holds its body at an angle, whereas Culex takes up a horizontal 

 position, as shown in Figure 53. The eggs (Fig. 54, D and E), 

 larvae (Fig. 54, A and B), pupae (Fig. 55), and adults differ also 

 in various ways, such as size and structure. 



Anopheles the Guilty Mosquito. To prove that the Anoph- 

 eles mosquitoes are guilty of transmitting the malarial fever 

 parasite an English physician had some of these insects sent to 

 him from a malarial district. He allowed them to bite him and 

 in due time he became a victim of the fever. Two other English 



