Using a modification of Kane's (1962, 1965) hexylenglycol (HG) isolation method mitotic apparatuses (MA) were isolated from spermatocytes of Pales ferruginea. The isolated MAs from metaphase had a greater dry mass concentration (d.m.c.) than those of prometaphase. In anaphase the d.m.c. was higher between the syntelic chromosomes and their poles than in the interzonal region. A nearly even d.m.c. distribution was observed in the partial spindle of amphitelic chromosomes throughout the whole of anaphase. In living spermatocytes the lower d.m.c. of the nucleus, as compared with the ground cytoplasm, disappeared within a few minutes after nuclear membrane breakdown. No apparent change in d.m.c. was observed during the rest of the division of these living cells and no changes comparable with those in isolated MAs were observed.