274 Sporozoa 



typical cephaline gregarines is equipped with an epimerite, or hold-fast 

 organelle, which varies in structure in different species (Fig. 6. 2). The 

 multiple "epimerites" of Nina gracilis (Fig. 6. 2, F) are filaments se- 

 creted after the organism becomes attached by means of its expanded 

 protomerite (37). The epimerites of certain species remain embedded in 

 a tissue cell as the trophozoite emerges and the parasite may remain at- 

 tached through much of the growth period. In other cases, the epimerite 

 adheres to one or more epithelial cells. The epimerite is commonly, al- 

 though not always, lost when the gregarine becomes detached from its 

 anchorage. An analogous structure, the mucron (Fig. 6. 2, C, E), is present 

 in certain acephaline gregarines, and a sucker-like depression lies at the 

 anterior end of various others (Fig. 6. 12, A, B, F). The mucron serves 

 for attachment in such species as Rhynchocystis pilosa (133), but may be 

 rudimentary and apparently non-functional in other cases. 



The trophozoite of the Schizogregarinida may either undergo merog- 

 ony, or give rise to one or a few gamonts (gametocytes). Since merogony 

 does not occur in Eugregarinida, surviving trophozoites develop into 

 gamonts. The gamonts of typical Gregarinidia become associated in pairs 

 or sometimes larger groups, a condition known as syzygy (Fig. 6. 3, A-C). 

 In many species, syzygy occurs early so that the trophozoites, immature 

 at first, are associated for some time before the differentiation of gamonts. 

 In other cases, association occurs much later and gamonts are differen- 

 tiated almost immediately afterward. In syzygy of cephaline gregarines 

 the anterior end of one sporadin (the satellite) often adheres to the 

 posterior end of another (the primite). Occasionally, two satellites may 

 be attached to one primite, and in exceptional cases several individuals 

 may form a chain. Such chains appear to be temporary associations. 



Development of mature trophozoites into gamonts often involves no- 

 ticeable changes. Autotomy of a posterior portion of the body precedes 

 syzygy in Rhynchocystis pilosa (133), and elongated organisms tend to 

 round up. The epimerite of cephaline gregarines, if not already lost, 

 undergoes partial or complete resorption; likewise, cuticular decorations 

 disappear. The associated gamonts — usually two, occasionally three — se- 

 crete an enclosing membrane to produce a gametocyst. In some genera — 

 Hentschelia, Lecythia (85), and Nina (37, 79) — a gelatinous or mucous 

 ectocyst encloses the usual membrane. Within the cyst each gamont under- 

 goes gamogony (Fig. 6. 3, D). In such genera as Hentschelia, Lecythion, 

 and Nina, gametocysts are voided from the gut at an early stage so that 

 gamogony, and subsequent syngamy and sporogony, take place outside 

 the host. In Carcinoecetes and Cephaloidophora, the gamonts apparently 

 leave the intestine early in syzygy, often becoming attached to the exo- 

 skeleton of the crustacean host and developing a gametocyst as "ecto- 

 parasites" (5). 



The original cuticle of each gamont persists within the gametocyst of 



