Hexacotyle extensicauda n.sp., a monogenetic trematode from the gills of the tunny (Thunnus thynnus L.)

This description is based upon a study of six identical monogenetic trematodes which were collected from the gills of the tunny by Mr F. S. Russell, F.R.S., and which were presented to the writer for identification. They had been fixed already in a flexed but otherwise excellent condition in Bouin's fluid on cleanly cut pieces of gill tissue to which they were adherent. Two of the specimens were cut into serial sections while still in situ on the gills, and the remaining specimens were detached carefully from the gills and examined whole. Gill tissue of the fish in the vicinity of the parasite was seen to be modified and such observations as could be made on the effect of the parasite on the tissues of the host have been recorded.