252 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 
convexly, both antero-posteriorly and supero-inferiorly, the cross-section 
of the sporoplasm at this point being unequally biconvex-lenticutar. 
Anteriorly, however, each lateral surface is probably excavated for the 
lodgment of the posterior end of the capsule of the same side. The 
cross-section ot the sporoplasm at the level of the infero-median cornu 
is a biconcavo-convex isosceles triangle. Superior surface convex in 
all directions with its postero-lateral margin coincident with the same 
margin of the inferior surface; differing from that surface mainlyin the 
slighter coneavity of the antcro-lateral margins (and the consequently 
less mucronate shape of the supero-lateral cornua) and in the greater 
extension forward both of the supero-median and of the supero-lateral 
cornua. The supero-inferior intercornual ridge mentioned above curves 
(in the vertical plane) from the supero-median cornu downward and 
backward through the interior of the shell cavity to terminate in the 
infero-median cornu. 
Micro-chemistry.— Hydrochloric acid aleohol carmine stains the nuclei 
better than other reagents. Iodine (aqueous solution with potassium 
iodide) stains the vacuole dark brown; stain removed by alcohol; stain- 
ing most intense at first, the vacuole staining more rapidly than the 
sporoplasm. This reagent causes the separation of the tail from the 
body, and a beaded appearance of the tail. As, however, | have not 
detected this condition in other examination media, I suspect that it is 
not the normal structure. Finally iodine renders the capsular walls 
transparent and the filaments visible. Sulphuric acid (cold, concen- 
trated) dissolves the tail (the shell remaining unaffected) and causes. 
the valves to gape open, and finally to separate. Gently warmed, no 
further effect is produced. Heated to the boiling point, the valve sub- 
stance is destroyed (dissolved ?). Ammonia water renders the capsular 
walls transparent and the filaments visible. Balsam renders the tail 
invisible, the shell remaining visible. 
Habitat.—Eneysted on head of Hybognathus nuchalis Ag. (identifi- 
cation by Prof. B. W. Evermann), collected November 24, 1891, in the 
Neches River, 14 miles east of Palestine, Texas, by Prof. B. W. Ever- 
mann, U.S. Fish Commission. Water temperature 9:4° C, (49°5° F.), 
Disease very frequent. 
Hffects—Although the tumors form quite extensive patches, the 
effect upon the fish could hardly, I think, be serious. That the move- 
ments of the jaw are not materially impaired is shown by the excellent 
nutrition of the fish. Indeed the present species seems rather a sub- 
commensal than a true parasite. Thélohan! reports that he saw acyst 
shell out of its place in the tissue of the fish and fall into the water. 
Everything implies that a similar process takes place here, as super- 
ficial pitted scars were seen upon several specimens. These show no 
trace of long-continued ulceration, being very free from the puckerings 
1 Annal. de Microgr., 1890, 11, pp. 203-4, 
