Protozoa from Fishes. 387 



cell-body. The cytoplasm stainsjblue and the nucleus dark 

 blue. These cells are commonly found clumped together in 

 groups ; hence the common idea that they function in the 

 clotting of the plasma. About 3 °/ are present. 



The parasites in the blood of the mackerel are found in the 

 medium lymphocytes and in the mature erythrocytes, and 

 seem to be two totally different forms, although, as will be 

 seen later, they may be only sexually differentiated forms of 

 the same parasite. Occurring in the lymphocytes were oval 

 forms, all within certain limits of the same size, viz., about 

 9 fiby 5fi (see PI. XVII. tig. 1, 1 & 3). They occupied the 

 side of the lymphocytes where there was most cytoplasm, and 

 compressed the nucleus, so that in larger forms this oro-an 

 was represented as a mere rim at the edge of the host-cell. 

 As a rule, however, the parasite occupied less than half the 

 area of the host-cell. The cytoplasm of these organisms 

 stained a fairly deep blue by the Komanowsky method, and 

 was slightly vacuolated. At about the middle of the cell- 

 body there was situated a large compact nucleus, containing a 

 conspicuous organella or karyosome, which was sometimes 

 situated some little way outside the nucleus. 



A few metachromatinic granules were to be seen scattered 

 in the cytoplasm. In some cases two parasites were found in 

 a single lymphocyte, and these were always close together 

 and on the same side of the host-cell nucleus (see PI. XVII. 

 fig. 1, 2). A blood count showed about 3 °/ of the lympho- 

 cytes to be infected. These organisms bore a striking 

 resemblance to the true rounded leucocytozoa found in the 

 lymphocytes and erythroblasts of different species of finches. 

 They were not in the least haemogregarine-like, displayed no 

 distinct capsule, and in their action towards the nucleus of 

 the host-cell were very similar to Leucocytozoon fringilli- 

 narum. All the organisms were, moreover, of the same type 

 and seemed to be maciogametocytes. They occurred alone 

 in one fish, not accompanied by the other parasites to be 

 described, and were not found free in the plasma or in any 

 other blood-cell. The organisms are interesting from the 

 fact that they are the first of their kind to be demonstrated 

 in the leucocytes of fish. As in birds, they were characterized 

 by their comparative abundance in the blood — a characteristic 

 but rarely found in the genus Hcemogvegarina. Occurrino- 

 together with the organisms above described in two other 

 fish and by themselves in another fish, parasites of a different 

 type were found in the erythrocytes (see PI. XVII. fig. 1 

 4 & 7). These were smaller than the " Lymphocytozoa" and 

 in general contour resembled small Halter idui, the parasite at 



