The author studied the carbon particle phagocytosis of ascitic phagocytes of mice, rats, chicken, rabbits and dogs by means of tissue culture, and obtained the following results: 1. In ascites there are a certain number of phagocytes series each of which possesses a common characteristic, and according to their size and shape these series can be classified into a small type-, an intermediate type-, a large type-phagocytes, and a large histiocytic phagocytes. These cells show various grades in their phagocytosis capacity, and judging from their phagocytosis capacity and other cell-functions, the small type phagocytes are the immature type, the intermediate type and the large type phagocytes are the mature type, and the large histiocytic ones are the aged type. 2. The patterns of the distribution of carbon particles phagocytosed in the cell may be divided into four types, Types I to IV, and these distribution patterns are interchangeable according to the degree of the cell maturity. 3. Considering these ascitic phagocytes of each species of animals from their lineage, the higher the species of animals the higher is the phagocytosis capacity and also the capacity to arrange the ingested carbon particles in a rosette formation becomes stronger, presenting a characteristic similar to monocytes.