Protozoa from Fishes. 385 



without any food until the 30th of July, and were still alive 

 when some were taken out and preserved in alcohol. Sections 

 were cut and stained with Giemsa, and, although the leeches 

 had not been on a fish for thirty-five days, their dorsal blood- 

 vessels were found to be crammed with parasites, which were 

 taken to be sporozoites of IJcemogregarina (see PI. XVI. fig. 2). 

 Examination of the gut })roved negative. There was not a 

 trace of a blood-cell of any kind left, the gut being full of 

 bacilli, the most common being a short slender rod. 



The account given by Reichenow of the development of 

 the Hsemogregarine of the tortoise does not in the initial 

 stages correspond with my observations in Cottus. There 

 was no evidence in the spleen of the fish of the two arms of 

 the parasite fusing to form a bean-shaped macroschizont. It 

 is more than likely that the parasite is liberated in the blood 

 as a free vermicule, where it finds its way to the spleen after 

 the manner of a " schizokinete." The fusion of the two 

 arms of a parasite was never seen either in the blood of the 

 fish or in its spleen (see Minchin & Woodcock). 



A large tumour, evidently a H?emangioma, was found on 

 one of the infected Cottus, and, although many of the blood- 

 cells in this tumour contained Haemogregarines, it would be 

 difficult to say whether or no they were the cause of the 

 growth. 



Parasites of Scomber scomber (the Mackerel). 



For examination for blood-parasites ten mackerel were 

 obtained at CuUercoats on August 26th, 1915. The fish 

 varied in size from 26"4 cm. to 32" cm. No external para- 

 sites were found on them. 



Only blood-smears were taken from each fish, since previous 

 examinations had been so disappointing, and it was not 

 thought worth while to make smears of spleen, swim- 

 bladder, etc. 



Four of the ten mackerel were found to be infected with 

 blood-parasites. Two individuals of these four were infected 

 with different parasites, whilst the other two were infected 

 with both of the parasites. Before going into details in 

 regard to the morphology of these parasites, it may perliaps 

 be of service to give a short description of the cellular 

 elements of the blood of a fish such as the mackerel. These 

 elements fall naturally into two groups — erythrocytes and 

 leucocytes — the former constituting by far the greater portion 

 of the corpuscles in the plasma. Erythrocytes in the 

 mackerel are oval in contour, rather more pointed at their 



