386 Mr. T. Bentliam on some 



ends tlian those of other fish, ami measure ronglily 12-13 ;;t 

 in leiiiith by about i> yu. in breadth. About the eentre of the 

 ctll-budy is a comiJaralivel}- small nuekus, staining dark 

 blue. Besides these eieujents are a certain number of 

 crythroblasts or immature red-cells. These are characterized 

 by being slightly smaller and more rounded than the erythro- 

 cytes, and by staining blue instead of, as in erythrocytes, 

 jiink by the Romanowsky method. The uuclei ol' these 

 cells are comparatively larger than those of erythrocytes., 

 but in no way ap[)roacli the size attained by those in birds ; 

 hence they cannot possibly be confused with medium lympho- 

 cytes. 



The leucocytes, if we include thrombocytes, are of six 

 ditlereut kinds — small, medium, and large lymphocytes, 

 eosinophils, mast-cells, and the thrombocytes above men- 

 tioned. 



The lymphocytes are in smear preparations all rounded in 

 shape, with a single nucleus which is always excentric in 

 position in the cytoplasm. In the small and medium forms 

 the nucleus occupies nearly the whole of the cell, there 

 being merely a thin ring of cytoplasm round the edge. In 

 the huge forms the nucleus is relatively small, being in 

 diameter not more than one-third of the diameter of the 

 whole cell. The small forms measure only about 8 /x in 

 diameter, the medium about 12 /i, and the large from 18-20 //.. 

 In all, the cytoplasm stains pale blue, the nucleus purple, by 

 the Romanowsky method, and they constitute about 15 °/q of 

 the cellular elements of the blood. 



Eosinojjhils arc small in the mackerel compared with 

 those of other groups. They are rounded in shape and 

 measure about 8 fi in diametei', have a single excentrically 

 placed nucleus, and their acidoj)hil granules are rounded and 

 occupy a fairly large space of cytoplasm on one side of the 

 nucleus. They are only slightly more numerous than the 

 next type. Mast-cells are slightly larger than eosinophils. 

 They stain a pale blue and do not seem to possess any 

 nucleus. In place of this there are scattered about in the 

 cytoplasm a moderate number of ruunded, ])urplish, deeply 

 staining granules which vary considerably in size. They 

 occur very rarely in films, there being about one or two iii 

 each smear. Thrombocytes in fish are fairly constant in 

 shape, and are to be recognized by both their elongated 

 fusitorm shape and their elongated centrally placed nucleus. 



They are in length about 12 /x, but only about 5 /a in 

 breadth at their widest jjart. Tlie nucleus measures about 

 7 /A by 5 /x, so that at its widest part it touches the edge of the 



