In order to study the influence of pressure effects on the cell division of sea urchin eggs we have performed a series of experiments to enable us to understand the meaning and the importance of morphogenesis of the embryo. Sea urchin eggs used are of Temnopleurus tereumatics, in the stages of unfertilization to early blastulae. The experimental results can be summarized as follows. 1) In unfertilized eggs the elevation of fertilization membrane is delayed by high pressure of 300 kg/㎠ applied for 15 minutes. The delay is in proportion to the pressure intensity and duration. Neverthless, furrowing process of the egg does proceed after the pressure is withdrawn. 2) Likewise, in fertilized eggs, the furrowing are retarded under high pressure, in fertilized eggs, the furrowing are retarded under high pressure, in proportion to the pressure intensity and duoration. In most cases, however, the rate of the cell division catches up with that of the control before reaching the stages of bastulae. 3) The deformities of pluteus can be observed in applying the pressure neither to unfertilized, nor to fertilized eggs in all stages.