This sub-class has been established by Schneider for the genus Ophryocystis, represented by two species, O. Biitschlii, from the Malpighian vessels of B/aps, and O. Francisci from Akis. The hosts are beetles belonging to the family Tenebrionidae. The organism is amoe-biform, with granular protoplasm, and more or less hyaline pseudopodia-like processes, sometimes simple, sometimes branched, and probably endued with extremely slow contractility. It is nucleated; small individuals are uni-nucleate, larger multi-nucleate. The nucleus appears to be vesicular with one or two nucleolar spots. The multi-nucleate masses become spherical and divide into a number of uni-nucleate individuals, connected to one another at a central spot by clear or somewhat granular prolongations. They throw out pseudopodia-like processes from their broader ends, and are detached by degrees from one another; the connecting prolongations are slowly absorbed. Two uni-nucleate individuals have been observed to conjugate and encyst. The cyst has a simple wall in O. Francisci, but its contents give origin to a number of coats, one within the other in O. BiitschliL It is marked by an equatorial line, along which it separates into two portions. The outer coats in O. Biitschlii do so whilst their successors are forming.
The two nuclei give origin to six, and then the central region, with two of the nuclei which probably conjugate, is converted into a spore; the remaining nuclei and protoplasm degenerate into residual masses, which disappear. The ripe spore is elliptical with pointed poles; it has a double spore-membrane; its contents divide into eight (?) uni-nucleate falciform bodies and a 'nucleus de reliquat.' It is rare for a cyst to contain two spores.
There are three Sporozoans included in this subclass - two, Miescheria and Sarcocystis, which are found within the striated muscle fibres of certain mammals, and one, Balbiania, recently discovered in the sub-mucous coat of the large intestine of a Macropus penicillatiis. The two first are most commonly found in the diaphragm, walls of the abdomen, eye-muscles, tongue, and the muscles of the thorax. The heart, pharynx and larynx are also favourite localities. They occur in various Mammals, especially the Pig, and have been detected in the Fowl and some other birds. In size they usually range from 3 mm. downwards, but specimens Ģin. long have been seen in the Rat, 2in. in the Roe-deer. They are usually elongate and pointed at the ends, but if the muscle fibres in which they are lodged are detached they become ovate. Balbiania is sub-spherical.
There is a membrane, either delicate (Miescheria, Balbiania), or composed of close-set rods (Sarcocystis). The contents are gelatinous, protoplasmic, with a number of minute, refractile, fatty (?) granules and protoplasmic corpuscles or germs (?). Rotation round the longer axis and contractions have been observed in a Miescheria of the Pig by Waldeyer. In large specimens the contents, except at the two extremities, are broken up into a number of spores (?), polygonal from mutual pressure, but globular when set free. The polygonal bodies contain large numbers of reniform or semi-lunar germs, which in Balbiania at any rate are developed in the peripheral bodies at an earlier period than in the central, and are set free by the breaking down of the inclosing membranes. This is probably the case also in the two other genera. The germs are homogeneous or granular, and often contain a bright spot or vacuole at either extremity. The vacuoles have been said not to exist in fresh germs. No nucleus has been detected either in the germs, the bodies within which they are formed, nor in the parent organisms.
The Sarcosporidia are sometimes spoken of as 'Miescher's vesicles', or 'Rainey's corpuscles,' the names of their first discoverers in Germany and England respectively.