PRODUCTION OF CLEAVAGE BY SUPPRESSION OF THE POLAR BODIES IN ARTIFICIALLY ACTIVATED EGGS OF URECHIS

It was suggested in an earlier paper (Tyler, 1931b) that those eggs which do not ordinarily divide as a result of artificial activation could be made to do so by suppression of the polar bodies. This was based on the fact that upon activation by means of dilute sea water only those eggs divide that extrude no polar bodies. The other type of egg produced by artificial activation behaves very much like the normally fertilized egg in its initial reactions to the treatment, extrudes two polar bodies, but does not divide. The results of the experiments reported here show that the polar bodies can be suppressed in such eggs by means of a second treatment with dilute sea water and that the eggs then divide. When Urechis eggs are treated with dilute sea water the percentage of the activated eggs that divide after various lengths of exposure bears an inverse relation to the total percentage of activation (Tyler, 1931b). Thus exposures resulting in 100 per cent activation give no cleavage, and the eggs are all of the type that extrudes both polar bodies. This simplifies the task of re-treating such eggs, since no unactivated eggs and no eggs of the type that divides are present in the dishes. The percentage of activation can be determined at about ten minutes after the initialtreatment,and sincethe firstpolarbody appearsat thirty minutes at room temperature there is ample time for the second treat ment. The first attempts at polar body suppression were made by means of anesthetics such as ether, phenyl urethane, and chloretone in various concentrations. Low temperature was later tried, as was also hypertonic sea water. These agents gave variable results, and in general although the polar bodies were suppressed while the eggs remained under treat ment they often appeared later when the eggs were removed to normal sea water. Dilute sea water was then tried and this was found to be quite an effective agent for suppressing the polar bodies and producing cleavage. 218 Time after first treatmentLengt