Effect of Shearing Forces on the Cortex of the Fertilized Egg of Arbacia punctulata

Abstract

In previous communications 1 2 the theory was advanced that, after monaster formation, the cortex of the fertilized egg of Arbacia punctulata consists in part of a bound calcium compound. Data were presented showing that this labile combination can be broken down in the living cell by various chemical agents, with the subsequent release of free calcium ions. For detecting calcium release, use was made of the observation that the characteristic red pigment “granules”of the egg disintegrate in the presence of calcium or other divalent cations. 3 The purpose of this paper is to describe briefly two observations which indicate that, in addition to the chemical procedures discussed in the previous papers, simple physical means are capable of breaking down the cell cortex and causing calcium release.

When immature eggs, or mature unfertilized eggs, or fertilized eggs that have not reached the monaster stage of development, are slowly crushed by withdrawing the sea water from under the cover slip with filter paper, considerable flattening of the egg can occur without rupture of the cell membrane. The compression can attain such a degree that the cell in many places is only a few micra thick. The red pigment granules remain intact as long as the cell membrane is unbroken. The moment that the cell membrane ruptures, the sea water and protoplasm intermingle and the red chromatophores disintegrate. The results are quite different when fertilized eggs that have reached the monaster stage (10–12 minutes after fertilization) are compressed in a similar manner. The slightest pressure on this egg causes the red pigment granules to “explode”in the region of the cell where the pressure is applied. The cell membrane remains intact and many of the red chromatophores are unbroken.