Fig. 94.—The tail­less spore of Myxo­bolus mül­leri, with the polar bodies and their nuclei and the sporo­zoite. (After Bütschli.)

The term Myxosporidia, which at the present day is universally applied to the “psorosperm tubes,” was introduced by Bütschli in 1881, who studied not only the structure and development of the spores, but also the protoplasmic body of the parasites (fig. 96), and confirmed the occurrence of numerous nuclei. Many authors have made important additions to our knowledge of the Myxosporidia: Perugia, Thélohan, Mingazzini, L. Pfeiffer, L. Cohn, Doflein, Mercier, Schröder and Auerbach; while the presence of this parasite outside the class of fishes has become known through Lutz, Laveran, and others. The species causing disease in fishes have been described by Ludwig, Railliet, Weltner, L. Pfeiffer, Zschokke, Hofer, Doflein, Gurley, Plehn, Schuberg, Fantham and Porter. With regard to classification the works of Thélohan (1895) and Gurley (1894) may be mentioned.

Fig. 95.—Schematic representation of a spore of Myxobolus. One polar capsule has protruded its filament; two nuclei and a “vacuole” in the sporozoite. (After Doflein.)

Fig. 96.—Chloromyxum leydigi. Active trophozoite (parasitic in gall-bladder of skates, rays, dog-fish). Ect, ectoplasm; ps, pseudopodia; end, endoplasm; y, yellow globules in endoplasm; sp, spores, each with four polar capsules. × 525. (After Thélohan.)

The Myxosporidia live either free on the epithelial surface of hollow organs (gall or urinary bladder, renal tubules, but never in the intestine), or are enclosed in the tissues of their host. The gills and muscular system are their favourite habitat, but other tissues or organs may be attacked. Species of Myxosporidia are also known from Amphibia, Reptilia, and a few invertebrates.