THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 279 



VII. CYSTODISCUS Lutz, 1889. . ., ,,, 



Etymology not given. "^T^Tu^, ■ fv^ -^^ ^ f'>v>v» J>f- ti- yi^pX^\A:'^f. ■ PAj 1^ 

 Centralbl. f. Bakt. ii. Pavimt^nkde, y,p.88; t&., Gurley, 1893, Bull. U.S. Fish 

 Com. for 1891, xi, pp. 411-13; ib., Braiin, 1894, Centralbl. f. Bakt. n. Parasi- 

 tenkde, xv, p. 87. 



Definitwn. — Characters those of the fomily; type, 0. immersus. 



Whatever may be the ultimate taxouomic destination of the species 

 here inehided, the genus will, I think, stand, as it is the first in order 

 of priority, having the spore with the capsules in 2 grouj)s, and a 

 bivalve shell. 



97. Cystodiscus immersus Lntz, 1889. PI. 42, figs. 1-10. 



Centralbl. f. Bakt. u. Parasitenkde, v, pp. 84-88, figs. 1-10 separately and 

 subsequently; (7;., Gnrley, 1893, Bull. U. S. Fish Com. for 1891, xi, p. 413; 

 ih., Braun, 1894, Centralbl. f. Bakt. u. Parasitenkde, xv, p. 87. 



Cyst none. 



Myjcospondium. — Youngest forms unknown. Hoping to find them 

 in the tadpoles, Lutz examined about a dozen, but the gall-bladders 

 were entirely free; in frogs and toads only a little larger, however, 

 myxosporidia were found, but they (even the very small ones, less 

 than 04 mm. in diameter) already showed the stiff disk form. In 

 numbei% usually several, often very many (30 to 50), visible through the 

 bladder wall, appearing macroscoi)ically as round transparent disks or 

 leaflets, as thin as pai)er, with frequently a whitish border in which the 

 upper and under surfaces meet directly (without the intervention of a 

 lateral surface as in a cylinder) ; upper and under surfaces very slightly 

 convex, the thickness being only -^^ to -^\- of the diameter; body-form 

 thus feebly biconvex lenticular, ranging in diameter Itom the limits 

 of visibility to 1-5 or 2 mm. 



Ectoplasm forming a plainly perceptible, transparent, structureless 

 membrane, completely resistant to the bile and noticeably so to chemi- 

 cal reagents, disintegrating on prolonged immersion in water; preserv- 

 ing the form of the organis;m which otherwise almost certainly would, 

 on account of its great thinness, become wrinkled and folded, but 

 whose borders have a subcircular outline. Ectoplasm often containing 

 great numbers of micrococcus-like bodies, which, as they brown only 

 very slightly with osmic acid, can scarcely be pure fat. They also can 

 not be cell-nuclei. 



Endoi)lasm containing numerous large vesicles, polygonal-flattened 

 by mutual pressure, producing the appearance of a cellular structure. 

 Vesicles possessing a subglobular coiitoui-, showing no trace of a 

 nucleus; upon rupture of the ectoplasm, escaping spontaneously into 

 the bile, in which (also in alkaline solutions) they immediately vanish 

 under thel^yes of the observer, probably on account of the solution of 

 a delicate surrounding membrane and the subsequent solution of their 

 contents. Amuiboid movements arc completely excluded by the mem- 



