53 
the first febrile attack. If this view be true, then it 
follows that the gametes develop from forms already 
present in the system, viz., the asexual forms, and 
possibly the divergence into sexual forms takes place 
from the youngest form of the parasite, i.e., the spore. 
But it is possible that the divergence takes place at a 
stage previous to the youngest form of parasite, i.e., 
at a stage immediately succeeding the entry of sporo- 
zoits into the blood, so that we have from the first 
indifferent and sexual forms present, involving, indeed, 
the existence of three kinds of sporozoits. Sexual 
development has been supposed to proceed mainly in 
the internal organs, e.g., bone marrow ; but it is being 
gradually recognized that young forms of gametes are 
also found in the circulation. Let us suppose that 
we are now dealing with fully developed gametes in the 
blood. We shall proceed to describe the further 
changes undergone in the mosquito. The male cell 
is, as we have seen, called the microgametocyte ; the 
female cell, the macrogamete. These we can dis¬ 
tinguish in the blood. Further flagellation can be 
observed, i.e., the protrusion of so-called ‘ flagella,’ 
i.e., microgametes or spermatozoa. These £ flagella ’ 
break off and fertilize the female cell, the macrogamete, 
a process which has been seen in Halteridium of birds, 
but only once in man. 
This fertilized female cell or egg is known as a 
Zygote. At a slightly later stage it is called the 
Ver mi cuius or Ookinet (Figs, io and 14). Both these 
terms are suitable ones, for the first describes the fact 
that the zygote becomes worm-like in shape, and the 
second, that the zygote moves. The Vermiculus stage 
can be seen on the slide in the case of Halteridium, 
but in the case of malaria parasites, only by taking the 
blood from the stomach of the mosquito after a suitable 
