PARTHENOGENETIC MEROGONY OR DEVELOPMENT WITHOUT NUCLEI OF THE EGGS OF SEA URCHINS FROM NAPLES

¹ From the Stazione Zoologica, Naples, and the Biological Laboratory, Princeton University

1. The stratification, by centrifugal force, of the eggs of the four species of sea urchin occurring at Naples is described.

2. The non-nucleate parts of the eggs of all four species can be activated by parthenogenetic agents. They throw off fertilization membranes characteristic of the species, and begin to develop.

3. Development of the parthenogenetic merogones of Arbacia pustulosa is similar to that of Arbacia punctulata.

4. The parthenogenetic merogones of Parechinus and Paracentrotus develop by a process of progressive fragmentation inside the fertilization membrane, similar to that occurring in the parthenogenetic normal egg which leads to normal free-swimming blastulæ.

5. Cleavage may take place in whole eggs while the nucleus is still intact.

6. Certain changes take place in the immature egg similar to those of the mature egg when treated with parthenogenetic agents.

7. No further development of eggs without nuclei has yet been obtained beyond the blastula.