THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 279 
VII. CYSTODISCUS Lutz, 1889. 
Etymology not given. 
Centralbl. f. Bakt. u. Parasitenkde, v, p. 88; ib., Gurley, 1893, Bull. U.S. Fish 
Com. for 1891, x1, pp. 411-13; ib., Braun, 1894, Centralbl. f. Bakt. u. Parasi- 
tenkde, Xv, p. 87. 
Definition.—Characters those of the family; type, C. immersus. 
Whatever may be the ultimate taxonomic destination of the species 
here included, the genus will, I think, stand, as it is the first in order 
of priority, having the spore with the capsules in 2 groups, and a 
bivalve shell. 
97. Cystodiscus immersus Lutz, 1889. Pl. 42, figs. 1-10. 
Centralbl. f. Bakt. u. Parasitenkde, v, pp. 84-88, figs. 1-10 separately and 
subsequently; ib., Gurley, 1893, Bull. U. 8S. Fish Com. for 1891, x1, p. 413; 
ib., Braun, 1894, Centralbl. f. Bakt. u. Parasitenkde, xv, p. 87. 
Cyst none. 
Myxosporidium.—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 0-1 mm. in diameter) already showed the stiff disk form. In 
number, usually several, often very many (30 to 50), visible through the 
bladder wall, appearing macroscopically as round transparent disks or 
leaflets, as thin as paper, 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 35 to +4; of the diameter; body-form 
thus feebly biconvex lenticular, ranging in diameter from 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 organism 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. 
Endoplasm containing numerous large vesicles, poly gonal-flattened 
by mutual pressure, producing the appearance of a cellular structure. 
Vesicles possessing a subglobular contour, 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 the eyes of the observer, probably on account of the solution of 
a delicate surrounding membrane and the subsequent solution of their 
contents. Amceboid movements are completely excluded by the mem- 
