With the purpose to study the influence of anemia in mother animal on the hematopoiesis of embryos, the author performed some fundamental experiments on the peripheral blood and the hematopoietic organs of the embryos, newborns from normal guinea pigs, the mother animals, and compared these findings with those on the blood picture of human as well as of other mammalians reported by predecessors. The results are as follows: 1. The average blood count of mother guinea pigs proved to be: erythroecyte count, 489 × 10 ⁴ / ㎣ ; Hb content, 83 per cent; the leucotyet count, 7,5000/ ㎣ ; and the percentage of leucocytes is; multinuclear leucocytes, 17.6 per cent; eosinophils, 4.6 per cent. 2. In some mother guinea pigs during pregnancy slight anemia occurs about second week of pregnancy, and continuing throughout the pregnancy, it recovers at the terminal stage. But the majority of mother guinea pigs actually become raher polycytaemic on conception and recovers to normal level immediately before delivery. 3. During the embryonal stage the erythrocyte series in guinea-pig embryo already shows the count of 466 × 10 ⁴/ ㎣ (with Hb, 75% ), and without showing any great change, it grows up to newborn. As for the blood count in the newborn immediately after birth, the erythrocyte count is 498 × 10 ⁴ / ㎣ and Hb is 81 per cent. About 12-24 hours after birth there is a transient increase in the blood count what is thought to be due to dehydration. 4. Scarcely any leucocytes appear in circulating blood during the embryonal stage, and around the fourth embryonal week the nucleated cell count is 10,000, and on the fifth week, 9.8000, but most of them are nucleated erythrocytes, decreasing rapidly from about 7 th to 8 th week. The leucocyte count in the 10 th week is barely is barely 530 / ㎣ . The leucocytes immediately after birth double in number due to leucocyte discharge from bone marrow, and multinuclear leucocytes increase in number. The average leucocyte count of the newborn guinea pigs is 1,9000 / ㎣ . 5. The resistance of erythrocytes in embryo against saline solution is weaker than that in mature animal erythrocytes, but in around the first to second week after birth it becomes rather resistant. 6. In observing slice specimens prepared from hematopoietic organs of embryos, and newborns, the erythrocyte series are produced in the liver and blood islands in about the latter half of the fourth embryonal week, and in about 5 th week in the liver and spleen, and next in the 8 th week the bone marrow hematopiesis appears, joining to the erythropoiesis in the liver and spleen. Through the 8th and 9 th weeks an increase in erythropoiesis of the bone marrow becomes pronounced, while the hematopoiesis in the liver and spleen decreases markedly, and in newborns mostly no such erythropoiesis in the liver can be recognized. Multinuclear leucocytes are produced in the liver and blood islands in the latter half of the fourth embryonal week, and in the 5 th - 6 th weeks they are produced in the liver and spleen, but their differentiation is extremely delayed, and also any of them hardly appear in the circulating blood. Next, by the 7 th week their production is commenced in the bone marrow. And they are well differentiated and many are of lobulated nucleus, but making the appearance only in a small number in peripheral blood until birth when they are all suddenly discharged into circulating blood stream.