CHANGES IN THE HEMOCYTE PICTURE OF GALLERIA MELLONELLA (LINNAEUS).

1. The hemocytes of Galleria mellonella (Linnaeus) larvae were identified and differentially counted in unfixed hemolymph with phase microscopy. The numbers of hemocytes per microliter of hemolymph were obtained from both unfixed and heat-fixed larvae. Hemolymph volumes were determined by the amaranth red method. These studies were made to determine what changes in the hematology occur as the last stage larvae pass through distinctive phases in transforming into pupae. 2. In differential counts, plasmatocytoids decrease, immature adipohemocytes suddenly appear, and mature adipohemocytes steadily increase. Spherule cells, oenocytoids and dividing hemocytes decrease as Galleria larvae develop into pupae. 3. The numbers of hemocytes per microliter of hemolymph increase as Galleria larvae proceed towards the pupal stage in both unfixed and heat-fixed animals. Counts were always significantly higher in heat-fixed than in unfixed larvae. 4. The hemolymph volume is the same in both unfixed and heat-fixed larvae. The hemolymph volume declines from about 34% (56.7 microliters) in precocoonspinning larvae to less than 16.4% (19 microliters) in newly formed pupae. 5. It is estimated from the various data presented that an average of 1,456,000 hemocytes remain in circulation within the hemocoele of unfixed larvae from the fifteenth through the twentieth days of life, and that with pupation more than one-half of these cells fall out of circulation. 6. In three out of 5 cases it was possible to correlate decreases in the plasmatocytoid population with increases in adipohemocytes. It is suggested that during the spinning of a cocoon plasmatocytoids transform into both immature and mature adipohemocytes, that when the larvae are densely cocooned mature adipohemocytes are largely formed by the maturation of immature adipohemocytes, and that in pharate pupae new mature adipohemocytes are derived from both immature adipohemocytes and plasmatocytoids. 7. The hemocyte picture of Galleria is compared to that of Prodenia and Bombyx. In all three of these Lepidoptera the plasmatocytoids decrease and the hemocytes with many polysaccharide and/or lipid or other types of inclusions increase prior to pupation. Galleria differs from the other two species in that their hemocytes with lipid or other inclusions do not appear until about the sixteenth or seventeenth days of larval life, do not divide, and in many cases are derived from circulating plasmatocytes.