[Illustration: FIG. 102.--Longitudinal section of a muscle of the domestic pig, with _Sarcocystis miescheriana_. × 30. (After Kühn.)] [Illustration: FIG. 103.--Transverse section of the muscle of a pig, with _Sarcocystis miescheriana_. × 38. (After Kühn.)] The Sarcosporidia usually appear as elongate, cylindrical, or fusiform bodies, rounded at both extremities and of various lengths and breadths (fig. 102). In some species they may be from 16 mm. to 50 mm. long, as in the sheep and roebuck. These bodies are the so-called sarcocysts or Miescher’s tubes. They lie in transversely striated muscular fibres which they distend more or less. The forms found in the connective tissue are apparently parasites which originally inhabited the muscular fibres, and only on disintegration of the fibres reached the connective tissue, where they grow to large oval or globular bodies (fig. 105). The mammalian muscles usually infected are those of the œsophagus, larynx, diaphragm, body-wall, and the psoas muscles. The skeletal muscles may be affected in acute cases, as well as those of the tongue and eye. The heart muscles are sometimes parasitized. In fresh material cut into thin slices the parasites are frequently recognizable, even with the naked eye, because of their yellowish-white colour. Under the microscope they appear to be coarsely granular (fig. 103). Beginners may find some difficulty in distinguishing them from other foreign bodies, such as dead and calcified encapsuled Trichinæ, or from Cysticerci that have died and become calcified in the early stages, more particularly as the Sarcosporidia also occasionally may become calcified. The Sarcosporidia are always enveloped in a membrane, which is probably formed at an early stage. In a few cases it remains thin and simple, in other cases a radially striated ectoplasmic layer is present (figs. 104, 108), which has been variously described. From the inner integument, which may be homogeneous or fibrous, thick or thin, membranes or trabeculæ pass into the interior of the body, forming anastomosing partitions, and so producing a system of chambers of various sizes that do not communicate with one another (figs. 104, 108). These chambers are occupied by sickle- or bean-shaped bodies (spores or sporozoites), or various developmental stages of them. The oldest spores are found in the centre of the Miescher’s tubes or trophozoites. If they are not liberated they die there, so that the central chambers of the tube are empty and hollow. [Illustration: FIG. 104.--_Sarcocystis miescheriana_ from pig. Late stage in which body is divided into numerous chambers or alveoli, each containing many spores. (From Wasielewski, after Manz.)]