[Illustration: FIG. 101.--Spore of _Hexactinomyxon psammoryctis_. At top of figure three polar capsules, one with polar filament extended. × 450. (After Stolč.)] Order. *Sarcosporidia*, Balbiani. The first member of this group was discovered by Miescher in 1843. This author found white filaments running parallel with the direction of the fibres in the voluntary muscles of mice. They were visible to the naked eye, and proved to be cylindrical tubes tapering at each end. They were as long as the muscular fibres, were enveloped in a membrane, and contained innumerable elongate or kidney-shaped bodies and a smaller number of little spherical forms. Th. v. Hessling confirmed (1853) the occurrence of these “Miescher’s tubes” within the muscular fibres, this author having discovered the same structures in the heart muscles of deer, cattle, and sheep. Both investigators considered them to be pathological transformations of the muscles. v. Siebold, from his own experiences, regarded them as fungus-like entophytes. Rainey (1858) discovered similar structures in the muscular system of pigs, and considered them to be early stages of _Cysticercus cellulosæ_, which error Leuckart rectified, simultaneously emphasizing their relationship with Myxosporidia. Both these authors found them in the muscular fibres, and both observed that they possessed a thick striated membrane. Manz (1867) published the results of more minute investigations on the structure and contents of the cylinders. This observer also recognized the disease in rabbits and attempted to cultivate the parasites. He also tried to induce experimental infection in guinea-pigs, rats, and mice, but the result was negative. However, domestic and wild mammals are not the only hosts of Sarcosporidia; these parasites are also harboured by birds. Thus, according to Kühn, they are found in the domestic fowl; according to Rivolta in _Turdus_, _Corvus_, and other birds; according to Stiles in North American birds; while Fantham found Sarcosporidia in the African mouse-bird, _Colius_. Reptiles also are parasitized occasionally. Bertram found them in the gecko, Lühe in the wall-lizard. It was found also that the Sarcosporidia could develop not only in the muscles but also in the connective tissue. This led to the foundation of a new, but provisional, classification by Blanchard, using the generic name _Miescheria_ for the parasites in the muscles and _Balbiania_ for those in the connective tissue. Finally, Sarcosporidia have also been observed in man. The relation of these parasites to certain diseases of domestic animals has been studied by veterinary surgeons. Sarcosporidia may cause fatal epizoötics among sheep. There is still a wide field open for research in regard to the structure and development of these parasites, and the manner in which the hosts become infected.