CLEAVAGE WITH NUCLEUS INTACT IN SEA URCHIN EGGS

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Abstract
In some cases, the nucleus remains as it is in the resting cell but nevertheless cleavage may take place and produce 2 quite normal "resting" cells. This has been found to occur in centrifuged eggs which have been stimulated to develop parthenogenetically by treatment with hypertonic sea water for 5-15 minutes. After one half to one hour, the egg nucleus remains unchanged, but a cleavage plane may form between the nucleate and non-nucleate parts of the cell, just as it does in such eggs when fertilized, resulting in 2 cells. This has been found to occur in Sphaerechinus granularis, Psammechinus (Parechinus) microtuberculatus and in Arbacia punctulata and A. pustulosa. Only a few cases have been observed in the last 20 years. No further development or change has been observed, and it has not been possible to produce such a cleavage lacking nuclear change by any chemical substances tried.