252 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



convexly, both antero-posteriorly aiul su])ero-iiif'oriorly, the cross-section 

 of the sporo])lasin at this ])oiiit being" unequally bicouvex-lenticutar. 

 Anteriorly, however, each lateral surface is ])robab]y excavated for the 

 lodgment of the i)osterior end of the capsule of the same side. The 

 cross-section ot the sporoplasni at the level of the infero-niedian cornu 

 is a biconcavo-convex isosceles triangle. Superior surface convex in 

 all directions with its posterolateral margin (joineident with the same 

 margin of the inferior surface; dift'ering from that surface mainly in the 

 slighter concavity of the anterolateral margins (and the consequently 

 less mucronate sliai)e of the su])ero lateral cornua) and in the greater 

 extension forward both of the supero-median and of the superolateral 

 cornua. The supero-inferior int ercornual ridge menfioned above curves 

 (in tlie vertical ])la!ic) from the supero median cornu downward and 

 backward throngli rhc interior of the shell cavity to terminate in the 

 infero-median cornu. 



Micro-cliemistry. — Hydrochloric acid alcohol carmine stains the nuclei 

 better than other reagents. Iodine (aqueous solution with ])otassium 

 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 sei)aration of the tail from the 

 body, and a beaded appearance of the tail. As, however, I 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 (told, 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, — Encysted on head of Hi/hognathns nuchalis Ag. (identifi- 

 cation by Prof. B. W. Evermann), collected November 24, 1891, in the 

 Neches Kiver, 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. 



Ejfects. — 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. Thelohan ^ reports that he saw a cyst 

 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 pnckerings 



1 Annal. de Microgr., 1890, ii, pp. L'03-4. 



