160 J. 0. WAKELIN BAKRATT AND GEORGE ARNOLD. 



the cytoplasm of these cells is coarser in Dytiscus than in 

 Hydrophilus. Small rouud-cells are present in the blood 

 in much smaller number than are phagocytic cells, varying 

 from one in fifty to one in thirty of the total number in 

 Dytiscus, and amounting to one in fifty or less in Hydro- 

 philus. 



In the phagocytic cells, a series of interesting changes 

 follow the ingestion of solid particles, which may now be 

 described in some detail. 



In Dytiscns the ingestive activity of these cells is very 

 great. Thus, if a solution of Indian ink be injected into the 

 abdominal cavity, it can be seen that after a few hours most 

 of the phagocytes have particles of the ink in their cytoplasm, 

 as is illustrated by fig. 4 (four and a half hours after injec- 

 tion). As digestion proceeds a clear area appears round 

 each particle, becoming a well-defined vacuole later on. 

 (see figs. 4, 6 and 8). A part of the ingested matter is not 

 digested, being eventually ejected into the plasma. The 

 vacuoles sloAvly contract until they become indistinguishable 

 in the schaumplasma. The nucleus undergoes the following 

 changes during the digestion of ingested matter. The 

 chromatin becomes more plentiful (cf . figs. 6 and 7 with 1 and 

 4) ; the nuclear membrane invaginates here and there and 

 eventually the nucleus becomes multilobulate (see fig. 8) , some 

 cells being even polynuclear (see fig. 9). 



In Hydrophilus the changes which take place in the 

 cytoplasm after the ingestion of solid particles are similar to 

 those of Dytiscus. The nucleus undergoes only a slight 

 change, the chromatin becoming more diffuse and the linin 

 strands more apparent (cf. fig. 12 with figs. 13 and 14). 

 Lobulation of the nucleus does not occur. As in Dytiscus 

 some of the granules, representing probably indigestible 

 portions of the iugesta, are extruded from the cytoplasm and 

 discharged into the surrounding blood-plasma. The staining 

 reaction of the solid ingesta changes, for in the cytoplasm at 

 first these take the acid stain, later they are stained by a 

 mixture of the acid and basic stains, and ultimately, at the 



