252 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



couvexly, both antero-posteriorly and snpero-inferiorly, the cross-section 

 of the sporopLism at this point being nnequally biconvex-k^nticutar. 

 Anteriorly, however, each lateral surface is probably excavated for the 

 lodjiineut of the posterior end of the capsule of the same side. The 

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

 is a biconcavo-eonvex isosceles triangjle. Superior surface convex in 

 all directions with its posterolateral margin coincident with the same 

 margin of the inferior surface; differing from that surface mainly in the 

 slighter concavity of the antero lateral margins (and the consequently 

 less mucronate shape of the superolateral cornua) and in the greater 

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

 cornua. The supero-inferior intercoruual ridge mentioned above curves 

 (in the vertical plane) from the supero median cornu downward and 

 backward through rhe interior of the shell cavity to terminate in the 

 jnfero-median cornu. 



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

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

 iodide) stains the vacuole dnrk 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, I have not 

 detected this condition in other examination media, I susi^ect that it is 

 not the normal structure. Finally iodine renders the capsular walls 

 transparent and the tllaments 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 transiiarent and the filaments visible. Balsam renders the tail 

 invisible, the shell remaining visible. 



Habitat. — Encysted on head of Hyhognathus nuchalis Ag. (identifi- 

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

 Neches Eiver, 14 miles east of Palestine, Texas, by Prof. B. W. Ever- 

 mann, U. S. Fish Commission. Water temperature 9'4o C. {i?r5'^ F.), 

 Disease very frequent. 



Effects. — 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 puckeriugs 



1 Annal, de Microgr,, 1890, ii, pp. 203-4. 



