DIPTERA 809 



each with a rounded mass of protoplasm about it, and finally the corpuscles are 

 broken down and these rounded bodies are liberated in the plasma as spores which 

 are known as merozoits. These spores infect new corpuscles, where they again 

 go through the stages of schizonts and merozoits, and thus the asexual cycle 

 is continued. The malarial paroxysm is coincident with sporulation. 



Parallel with the asexual cycle sexual elements or gametes are produced by 

 schizonts. These sexual elements, however, can not copulate within the human 

 organism on account of the unfavorable temperature. To enable them to carry 

 out this function, and to develop further they must be transferred to the aliment- 

 ary canal of an Anopheles, which is done when one of these mosquitoes sucks the 

 blood in which they are. Here the union of the male and female gametes takes 

 place and there results a stage known as the migratory ookinete. The ookinete 

 penetrates the wall of the midintestine of the mosquito and there transforms to 

 the oocyst. In the process of growth of the oocyst further stages occur, first by its 

 division the sporoblasts, and from these, by ftuther division, the sporozoits, when 

 the oocyst is mature it bursts, liberating the sporozoits which thus pass into the 

 general body cavity of the host. The sporozoits now find their way into the sali- 

 vary glands of the host and there remain until the mosquito, in biting, forces 

 them along with the saliva, through its proboscis into a human being. Then the 

 asexual cycle begins in the blood of a new host. 



Aedes. — This is a very large genus of world-wide distribution 

 Dyar ('22) describes 73 species that have been found in the United 

 States. The species vary greatly in habits; but with most of them 

 the larvae develop from over-wintering eggs in early spring pools. 

 Some species, however, breed in water-barrels, and other artificial 

 containers ; one of these is the carrier of yellow fever. 



The yellow-fever mosquito, Aedes cBgypti, is distributed through- 

 out all tropical regions of the world and is often carried by commerce 

 into temperate regions. But as it is destroyed by frost it can not 

 become established where frosts occtu*. Hence outbreaks of yellow 

 fever in the North are checked naturally as winter approaches, and 

 with our present knowledge of the methods of control of this disease 

 it is not probable that it will be permitted to become epidemic again 

 in the United States. 



When yellow fever appears the patients should be kept in mosqui- 

 to-proof rooms, so that they may not serve as centers of distribution 

 of the disease ; and the breeding places of mosquitoes should be drained 

 or screened, or oiled. 



The yellow fever mosquito breeds in cisterns, water-barrels, 

 flower-vases, and in the various water receptacles about houses. The 

 life-cycle under favorable conditions is completed in from twelve to 

 fifteen days. This is essentially a domesticated species. It is rarely 

 found far from the habitations of man. 



The fact that yellow fever is transmitted by this mosquito has 

 been definitely established; but it is not certain that the causative 

 organism is known, although some investigators claim to have found 

 it. 



The yellow fever mosquito was first described by Linnaeus in 1762 under the 

 name Culex cegypti. But the Linnasan genus Culex has been divided and this 

 species pertains to the genus Aedes established by Meigen in 18 18; hence its 

 correct name is Aedes agypti. Unfortunately a score of other names have been 

 applied to it; those most commonly found are Aedes calopus, Stegomyia fascidla, 

 and Stegomyia calopus. 



