PHYSIOLOGICAL STUDIES OF DIFFERENTIATION IN MYTILUS EDULIS. I. THE OXYGEN UPTAKE OF ISOLATED BLASTOMERES AND POLAR LOBES

¹ Department of Zoology, University of California, Berkeley, California

1. The oxygen consumption of isolated blastomeres and isolated polar lobes of the eggs of Mytilus edulis was measured by means of the Cartesian diver microrespirometer. The average oxygen uptake of CD embryos is 0.78 ± .027 µl. O₂/hr./mm.⁸ CD cytoplasm. This is 13 per cent lower than the average oxygen uptake of AB embryos (0.90 ± 0.032) over a comparable period of development.

2. This lower respiratory rate of CD cytoplasm is undoubtedly due to the presence of the polar lobe cytoplasm. Isolated polar lobes have an oxygen uptake of 0.42 ± .025 µ1. O₂/hr./mm.³ cytoplasm, which is 25 per cent lower than the average oxygen uptake of whole eggs during the time of polar lobe formation (0.56 ± .013). Calculations by several methods suggest that the difference in respiratory rate between the polar lobe and the remaining egg cytoplasm may be appreciably greater than the above figure.

3. The rate of oxygen consumption of polar lobes remains constant after isolation from whole eggs whereas those of AB and CD embryos, as well as whole embryos, exhibit a gradual rise during subsequent development. Prior to hatching, whole embryos show a temporary decrease in oxygen consumption. This has been found to be due to a decrease in oxygen uptake of derivatives of the AB cell. Isolated CD embryos exhibit a steady rise in respiratory intensity during this period. This difference in rate of oxygen consumption of AB and CD embryos prior to hatching can, to some extent, be correlated with their rate of cell division.