not here...a sexual process...the result of which is the
motile vermiculus? This is a process which we might
have expected and which I am confident will be found
to occur in the case of the human malaria parasites...’
[30]. The significance of this observation initially eluded
Ronald Ross (see below) something that remained with
him for the rest of his life [31] but was not missed by
Patrick Manson who wrote to Ross that ‘MacCallum’s
observation on Halteridium; if it is correct, it is of the
greatest importance’ [31,32]. Here MacCallum reached a
dead end because he believed that the vermicule then
invaded cells of the vertebrate host but was unable to
pursue this line of investigation.