STUDIES ON A CORTICAL LAYER RESPONSE TO STIMULATING AGENTS IN THE ARBACIA EGG

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Abstract
Eggs of the sea urchin, Arbacia punctulata, have been treated with molar urea solution for periods of time ranging from 3 seconds to 21/2 minutes. In a few cases, molar solutions of thiourea, glycerine or sucrose were used. Tn the presence of these agents, Arbacia eggs exhibit essentially the same kind of visible cortical response as that obtained with sperm cells and other stimulating agents. Typically, the cortical response to non-electrolyte solutions results in the formation of a perivitelline space which is from two to three times as wide as that obtained upon insemination. Dissolution of the fert. membrane results from continued exposure to the non-electrolyte solution. Frequently, eggs treated with urea cleave when returned to sea water. These cleavages are irregular and give rise to but a few blas-tomeres. Since activation of the eggs in the presence of urea is incomplete, and since such urea-treated eggs in many instances may be inseminated and then cleave in a regular fashion, it is suggested that fertilization has, in such cases. been superposed upon incomplete artificial activation. Arbacia eggs which remain in urea for relatively long periods of time become amoeboid. The amoeboid activity of such eggs has been briefly described. The observations and results presented in this paper are essentially in agreement with the views considered in the earlier papers of the series.