BULLETIN OF THE UNITED STATES FISH COMMISSION. 41 



It is, of course, not possible with the material at present in my hands 

 to identify the species, nor can we do more than indulge in surmises 

 as to what must be the hosts in which the Redia or nurse stage of 

 the parasite resides. That probably is some moUusk abounding near 

 where the infested Gunners were taken. To make out the complete 

 life-history of the parasite which we are now dealing with would prob- 

 ably take several years, and would involve the necessity of a prolonged 

 residence in the localities wbero the infested fish were taken in order to 

 be able to trace the parasite from one host to another. All that we can 

 now be assured of is that the cysts contain a Cercaria in the encysted 

 or pupal stage, and that the parasite is one of many similar forms known 

 to infest fishes of the family of Cyprinidce, especially where the encysted 

 state also occasionally produces papules on the skin. 



The accompanying pathological effects produced by means of physio- 

 logical processes are of the greatest interest to the writer, and are signifi- 

 cant in connection with known facts relating to the movements of pig- 

 ment or color-bearing cells. These, as is well known, are specialized 

 differentiations of ordinary cells charged with black, brown, red, or yel- 

 low granules. Why the presence of the cysts should attract pigment 

 cells or cause them to be developed in places normally devoid of them 

 is the question raised by what we have learned from a study of the tis- 

 sue adjacent to the cysts. Normally, and for a very obvious reason, the 

 cornea of fishes is quite transparent, but the infested corneas of the 

 Gunners before us have pigment cells developed around the cysts, and 

 they thus partially intercept the light passing into the eye, as already 

 noticed. Where the cysts are numerous and adjacent, or nea/ly in con- 

 tact in the corneal tissue, the crowded masses of pigment cells produce 

 an opaque reticulum, in the meshes of which the cysts are lodged. But 

 aside from these the less densely aggregated pigment cells in the vicin- 

 ity are of the greatest interest, especially when studied in relation to 

 the structure of the cornea, the principal tissue of which is known to 

 be laminated and to contain cellular nucleated bodies, known as corneal 

 corpuscles of a flattened or depressed form, with long protoplasmic 

 processes extending out into capilliary spaces between the laminae, and 

 thus in stained preparations producing the appearance of a close net- 

 work of fine fibers when a prepared cornea is viewed flatwise by trans- 

 mitted light. The protoplasmic processes of the superimposed cor- 

 puscles existing between layers of a slightly different depth have a 

 tendency to run at right angles to each other, and the stained filaments 

 of corpuscles of different laminae therefore tend to divide the trans- 

 parent interspaces of the corneal substance into quadrangles. This is 

 precisely what happens in some cases with the pigment cells, which 

 have accumulated in the infested cornea of the Gunner. The color- 

 bearing plasma of the pigment cells seems, therefore, either to have 

 wandered into tlie corneal lacunae previously occupied by the corneal 

 corpuscles, and to have displaced them, or the corneal cori)uscles them- 



