The
life cycle follows a seasonal course. The earliest stages may appear in the
kidney any time between March and June. Growth proceeds and
sexual differentiation takes place but mature
gametes are not found until November, when the first stages of sporogony are first found. Mature spores containing sporozoites are formed in January and become increasingly common up to May. Degenerating stages of spores are common in summer. The earliest stages within the renal organ are 10
μm in diameter. To the naked eye the later stages of the parasite have the appearance of a rounded milky white dot. The
trophozoites appear opaque and occasionally granular.
Schizogony occurs in the host cell. Morphological sexual differentiation is not detectable until growth is almost complete. The
microgametocyte divides into 32
nuclei. At this stage cleavage of the
cytoplasm brings about the formation of
uninucleate cytomeres. Nuclear division again occurs within these and these latter divisions form the
microgametes. The microgamete possesses a dark centre and a lighter ring round the periphery and is released from the host cell.
Fertilization occurs within the
lumen of the renal organ. After fertilisation, a thick membrane forms outside the
zygote. The
nucleus assumes a characteristic
spindle shape and subsequently divides. Nuclear divisions proceed until numerous
cone shaped nuclei are found below the cell membrane. This cell membrane becomes folded and the nuclei sink in (the oocyst stage). Each is surrounded by a portion of cytoplasm to form a
sporoblast. A single nuclear division then occurs and the two nuclei elongate to form sporozoites each with a small cytoplasmic body. The
oocyst has numerous
sporocysts each with two
sporozoites. ==References==