808 AN INTRODUCTION TO ENTOMOLOGY 



The eggs are laid in boat -shaped masses or "rafts" on the surface 

 of the water of ponds of a permanent nature and on water of artificial 

 containers, as water-barrels. A larva of Culex is described and figured 

 above (Fig. 1020). 



Anopheles.- — To this genus belong those mosquitoes that have 

 been f ovrnd to be the carriers of malaria. Nine species oi Anopheles have 

 been found in the United States, of which four are known to be carriers 

 of this disease. In this genus the palpi of both sexes are nearly or 

 quite as long as the proboscis and the wings are frequently spotted. 

 When at rest on a vertical wall the body is usually held at an angle 

 with the vertical (Fig. 1024). Some species often enter houses. They 

 hibernate in the adult state and can be found during the winter in 



cellars. 



The eggs are laid singly in 

 small numbers upon the sur- 

 face of water. The larva 

 when at rest floats in a hori- 

 zontal position beneath the 

 surface film (Fig. 1025). There 

 is no respiratory tube but in- 

 stead a flattened area on the 

 Fig. 1025.— Normal position of the larvae eighth abdominal segment into 

 of Culex and Anopheles when' at rest. j^- j^ ^^^ ^^,^ spiracles open. 



Culex, left, Anopheles, middle; Culex tv ^ 1 • • n 1 



pupa, right hand figure. Malaria IS a well-known 



and widely distributed disease. 

 It is most common in the 

 vicinity of swamps, and is more virulent in the South than in the 

 cooler parts of the country. It is caused by unicellular parasites in 

 the blood which feed upon the red blood corpuscles. These parasites 

 belong to the genus Plasmodium of the Protozoa. Three species of 

 these malarial parasites are now recognized, each of which causes a 

 distinct type of malaria. 



The life-cycle of the malarial parasites is an exceedingly com- 

 plicated one. Our knowledge of it is the result of extended investi- 

 gations by several workers. The history of these investigations is a 

 most interesting one; but space can not be taken to narrate it here. 

 Accounts of these investigations, with details of the results obtained 

 are given by Howard, Dyar, and Knab ('12) and Riley and Johannsen 

 ('15). The following summary of the life-cycle is condensed from the 

 accotmts by these writers. 



The malarial infection is introduced into the blood circulation of man by 

 the bite of a mosquito that has previously bitten a person having this disease. 

 It is only certain species of mosquitoes of the genus Anopheles that transmit this 

 disease to man. The infecting organism, which in that stage of its development is 

 known as a sporozoite, penetrates a red blood corpuscle and becomes an amoeboid 

 schizont. This lives at the expense of the blood corpuscle and as it develops there 

 are deposited in its body scattered black or reddish black particles. These are 

 generally called melanin granules, but are much better referred to as hcemozoin, 

 as they are not related to melanin. The haemozoin is the most conspicuous part of 

 the parasite, a feature of advantage in diagnosing from unstained preprations. 

 As the schizont matures, its nucleus breaks up into a number of daughter nuclei. 



