[Chronology of the ultrastructural modifications during the growth of Gregarina blaberae]

In an ultrastructural study the development of the sporozoite as well as the growth and development of the trophozoite of Gregarina blaberae were followed in the course of experimental infections of larvae of the cokroach Blaberus craniifer. The spectacular growth involved the transformation within 18 days of the sporozoite, measuring 15 X 1 micronm, to a cephaline--trophozoite affixed to the intestinal epithelium--of 250 micronm length and 65 micronm diameter. The sporozoite's ultrastructure is not different from that of sporozoites of other Sporozoa studies to date--the conoid and dense bodies are present. The pellicle consists of 3 membranes, but there are some interruptions in the internal membrane complex. The first dictyosomes are formed from the nuclear envelope. The migration of the nucleus and of the dense bodies, followed by the regression of all the structures characteristic of the sporozoites, and the establishment of a cortical zone that comes to cover the epimerite, take place within 48 h after infection and mark the transformation of the sporozoite into the trophozoite. Development of the cephaline involves the formation of the epicytic folds, which occurs at the base of the deutomerite, starting on the 3rd day of development. A regular system of longitudinal or epicytic folds is formed over the entire surface of the gregarine. On the 4th and 5th days of development, a vacuolar system and a chondriome become differentiated in the epimerite, while a fibrillar septum separates the protomerite from the deutomerite. The next stage, starting on the 6th day, is characterized by distribution of polysaccharide reserves between these 2 segments. The model studied allows us to determine the role of the epimerite in the parasite's nutrition, as well as the development of the chondriome and of the cortical membranes in the course of the vegetative growth phase of the cephaline gregarine.