“The formation of the centrosome in enucleated egg-fragments”

To test whether the centrosome is a permanent cell organ or not, Professor E. B. Wilson (1901) made an experiment on the sea urchin egg by treating, with a salt solution, enucleated egg fragments obtained by shaking. He observed that asters containing centriole and capable of division were produced in the enucleated fragments. He, therefore, came to the conclusion that at least some of the centrioles in the asters thus formed must have arisen de novo. Some writers criticized his results, saying that the formation of the centrioles in the enucleated fragments observed by him might have been due to the shaking-out of the nuclear fluid into the cytoplasm. Wilson, therefore, suggested that his experiment be carried out by the author in a somewhat different manner—instead of shaking, to cut eggs singly and to treat the nucleated and enucleated pieces separately. The author tried this experiment on the egg of Cerebratulus in the summers of 1903 and 1904. Strict precautions were taken to prevent accidental fertilization, everything used for the experiment being sterilized. Individual eggs were cut into nucleated fragments (i. e., fragments containing the first maturation mitotic figure) and also enucleated fragments. The latter were kept for an hour in a solution of calcium chlorid. Then they were transferred to sterilized sea water. Asters were produced in almost all enucleated fragments thus treated. What is more striking, all the asters had centrioles which were identical with those found in the whole eggs subjected to the same treatment. The nucleated half was stained and was shown to have had the mitotic figure intact. From these experiments no other conclusion can be drawn than that the centrosomes, with centrales of the enucleated fragments, were formed de novo.