THE MYXOSPORIDIA, OR PSOROSPERMS OF FISHES. 253 
thus caused. Moreover they conform very closely to the shape of the 
cysts. This is especially well shown where a cyst situated in the center 
of a group has shelled out, the surrounding cysts, preserving the shape 
of the cavity. 
In this species, under influence of cold, concentrated sulphuric acid 
(which dissolves the tail) the valves separate, the divergence appear- 
ing always to begin at the posterior end. The appearances seem to 
favor the view that such divergence was the result of the previous 
solution of the tail, the 2 lateral pieces of which would thus act as a 
splint. As, however, examination of untailed species (in which I sus- 
pected the lateral pieces might exist without the median) failed to show 
evidence of the existence of the lateral pieces or even of the constancy 
of the initial posterior divergence, this function of the tail must be 
regarded as dubious. Inany case, at least, one other causal factor must 
be involved in valve separation, as iodine, which produces separation 
of the tail, does not produce separation of the valves. Isuspected that 
this might be exosmotic pressure from within, and attempted to produce 
valve separation by the action of strong glycerin used after iodine 
had detached the tail, but the results were indecisive. 
This species is particularly interesting as exhibiting decided supero- 
inferior asymmetry, the superior valve being conspicuously more con- 
vex, and the supero-median cornu projecting farther forward. It is 
also important to note that the tail is not a shell process, but is, on the 
contrary, an independent structure with distinct optical and chemical 
characters. 
76. Myxobolus sp. incert. 
Psorosperms of Coregonus fera, Claparede, 1874, in Lunel’s Hist. nat. des poissons 
d. bassin du Léman, p. 114. 
Cyst.—A single one seen, 1 mm. in diameter; contents entirely differ- 
ent from those of the other branchial cysts, approximating to, without 
being perfectly identical with, those of the cysts of the muscles of the 
same fish. 
Myxosporidium unknown. 
Spore.—Distinguishable from those of the muscle cysts by their 
shorter and usually single tail, which, however, in a great number of 
individuals was bifurcate at the extremity. 
Habitat.—Branchial arches of Coregonus fera. 
77. Myxobolus cf. linearis. Pl. 33, figs. 5-8. 
Cysts of base of dorsal fin of Ameiurus melas, Gurley, 1893, Bull. U. 8. Fish 
Com. for 1891, x1, p. 417. 
Cyst.—Subspherical, about 1 mm. in diameter, 7 in number in a row 
at the bases of the spines of the second dorsal fin. 
Myxosporidium unknown. 
Spore.—Body lanceolate; length of body, 19 4; breadth, 5 or 6 y; 
thickness, about 3 yp. 
