190 MOSQUITOES OF NORTH AMERICA 
fer from one host to the other. When a mosquito sucks the blood of an individual 
harboring gametes in a state of complete maturity, these, finding themselves in 
a temperature favorable to their further development, copulate. The male 
gamete or microgametocyte throws off prolongations in the form of flagella, 
called microgametes, and these seek to unite with the female gametes or macro- 
gametes. Upon contact with the microgamete the macrogamete prolongs its pro- 
toplasm, forming the so-called cone of attraction. This first stage, brought about 
by the union of microgamete and macrogamete, is designated as the odkinete and 
can be easily observed in any mosquito, or even in blood transferred from the 
human body directly to the microscope slide. However, the succeeding stages can 
only take place in the stomach-wall of an Anopheles, as demonstrated by Grassi. 
The odkinete, to undergo further development, penetrates into a cell of the 
stomach-wall of the transmitting insect and there transforms to the odcyst. 
In the process of growth of the odcyst further stages occur, first, by its division 
the sporoblasts, and from these, by further division, the sporozoits. When the 
odcyst 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 
salivary glands of the host and there they remain until the mosquito, in biting, 
forces them, along with the saliva, through its proboscis into a human being. 
Then the other, sporogonic, or asexual, cycle begins. 
The sporozoits when introduced into the blood at once enter the red blood- 
corpuscles and are now called schizonts. The schizont grows within the blood- 
cell and finally undergoes a process of division. The products of this division 
are called merozoits. These merozoits are liberated but at once enter another 
blood-cell where they again go through the stages of schizonts and merozoits. 
Parallel with this development the schizonts begin also to produce gametes or 
sexual elements. 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 require the intervention of 
an intermediary host, as already described. 
In the macrogametes there is furthermore to be observed a curious phe- 
nomenon first determined by Schaudinn; we refer to the parthenogenesis which 
is nothing less than a stage which insures the survival of the plasmodium. The 
macrogamete when mature, in order not to disappear from the organism, as 
happens with the microgametocyte, divides in the same manner as the schizonts. 
Probably each product of this division then again becomes a macrogamete. In 
this parthenogenesis of the macrogametes lies the explanation of the cases cf 
malaria with periodical attacks recurring at great intervals of time. This phe- 
nomenon has already been determined for Plasmodium vivax and Plasmodiua 
falciparum, and there is every reason to believe that the same occurs with 
Plasmodium malarie. An ancient Roman imprecation “ Quartana te teneat” 
is significant in this connection as it can be given no other interpretation. 
As already stated there exist three well-defined species of Plasmodium which 
cause human malaria: Plasmodium malaria, P. vivax and P. falciparum. For 
the diagnosis of the species two methods are employed. One is to examine a drop 
