THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 279 



VII. CYSTODISCUS Lntz, 1889. 



Etymology not given. 



Centralbl. f. Bakt. u. Parasitenkde, v,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. 



Definition. — Characters those of the family; type, (J. immersus. 



Whatever may be the ultimate taxonomic destination of the species 

 here included, the genus will, I tliink, 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. PI. 42, figs. 1-10. 



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

 subsequently; ii., Gurley, 1893, Bull. U. S. Fish Com. for 1891, xi, p. 413; 

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



Cyst none. 



Myjcosporidium. — 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 

 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 pa])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 -^q- 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-likc 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, polygonal-flattened 

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

 Vesicles possessing a sub globular 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. Amoeboid movements are completely excluded by the juem- 



