Devauchelle G. 1968. [Study of the ultrastructure of Gregarina polymorpha (Hamm) in syzygy] [Article in French]. J Protozool 15(4):629-36
The electron microscope study of syzygy in Gregarina polymorpha shows that this coupling, a prelude to cyst formation and to sexual phenomena, must not be considered as a simple pairing of individuals, but is rather the response of a gamont to a stimulus coming from another individual of a different sex. This response, in the species studied, can be recognized from the modifications that will appear progressively at the contact surfaces of the two gregarines. They affect only the protomerite apex of the posterior individual. There occur: rapid growth of the protomerite epicyte; separation of this epicyte from the fibrillar zone underneath; formation of a protomerite cup containing various inclusions; the disappearance of cuticular digitations and the formation of invaginations which become deeper and deeper.
All these modifications occur as soon as syzygy starts. They seem to indicate a reaction of the satellite epicyte to a possible stimulus coming from the anterior female gamont. This epicyte could play a different part from the initial one.
In the case of association between a primate and several satellites, the posterior gamonts react in a comparable manner but not together.
Tronchin G, Schrevel J. 1977. [Chronology of the ultrastructural modifications during the growth of Gregarina blaberae] [Article in French]. J Protozool 24(1):67-82
Excerpts: Development of the Trophozoite
3 days after infestation -The young gregarine measures 4-6 x 2-3 um. One can distinguish 2 parts: the epimerite embedded in the intestinal epithelium, and the proto-deutomerite free in the lumen. The smooth, primitive wall of the sporozoite begins to "puff up" at the posterior of the cephalines.
4 days after infestation -Trophozoite measures 10-20 x 5-7 um, and clearly shows 2 different parts, the epimerite covered in the manner of a "skullcap" and the proto- deutomerite constricting the brush border. Large numerous vacuoles in the epimerite often contain opaque material at their periphery, suggesting a digestive nature. The raised membranes form clear individual folds in the posterior.
5 days after infestation -A thin partition, the septum, individualizes the body of the parasite and separates it into 2 distinct parts (with three segments): the protomerite, a kind of a collar following the epimerite, and the deutomerite (posterior) containing the nucleus. Although most abundant in the part "distale(?)," folds are also in the protomerite, and are also present generally on the whole gregarine body. Rapid growth in the epimerite brings about a formation called "junction ring," "ring strip," or "epimerite ring." The septum, not well defined in this stage, is born in the middle of the parts and spreads around the periphery.
6 days after infection -3 compartments are clearly differentiated and adult stage is reached. Opaque vacuoles are contained in the periphery of the "medulaire(?)" zone of the epimerite. The septum is more distinct, constituted by an entanglement of fine fibers to a thickness of 0.4-0.6 um with a light convex shape towards the deutomerite, and branches in to the other 2 segments (it is not an impenetrable barrier).