The sexual stages
The action now moves to Canada in 1897 and to the
United States a year later where a medical student, William
MacCallum, and his colleague, Eugene Opie, while
examining the blood of crows infected with Haemoproteus
columbae, a haematozoan closely related to the
malaria parasites, observed flagellated structures which
they described in detail and also recorded how the flagellated
bodies fused with non-motile bodies to form a
vermicule (now called an ookinete) [27]. MacCallum
suggested that he was witnessing sexual reproduction
that paralleled that in mammals (and, it should be
noted, related sporozoans that were already familiar to
European zoologists [28,29]) and that the flagellated
forms were male gametes, the non-motile forms female
gametes and the vermicule the zygote. MacCallum’s
findings are very significant as he realised that: ‘Have we