PREFURROW BEHAVIOR OF THE EQUATORIAL SURFACE IN ARBACIA LIXULA EGGS*

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Abstract
Study of equatorial surface activity occurring immediately before furrowing in A. lixula (= A. pustulosa) eggs was undertaken to learn more about the establishment of the cleavage mechanism. Behavior of echinochrome granules in the egg surface was used as the indicator of surface events. An hour after fertilization A. lixula eggs were slightly flattened and periodically photographed until the furrow appeared. Measuring regional changes in the concentration of echinochrome granules showed that a band of equatorial surface .apprx. 22 .mu.m wide, which comprised 32% of the uncleaved egg surface, shrank about 34% and formed a densely pigmented band averaging 15 .mu.m wide. This contraction in the equatorial zone was accomaanied by expansion or stretching in the subequatorial surfaces. The possible relation between these events and formation of the microfilamentous contractile ring was discussed.