DEVELOPMENT OF HALF-EGGS OF ARBACIA PUNCTULATA OBTAINED BY CENTRIFUGING AFTER FERTILIZATION, WITH SPECIAL REFERENCE TO PARTHENOGENETIC MEROGONY

¹ From the Marine Biological Laboratory, Woods Hole, and the Biological Laboratory, Princeton University

1. Fertilized eggs of Arbacia may be broken by centrifugal force into white and red halves similar to the unfertilized egg; the nucleus is in the white half.

2. The white half may develop quite normally through the blastula stage; no normal plutei have been obtained. The first two blastomeres may develop independently forming white twins. Amoeboid forms and loose masses of cells also result from the white half.

3. The red half does not cleave or develop. It may become amoeboid or notched, or form asters, thus indicating activation.

4. It makes little difference at what stage the eggs are centrifuged.

5. The red half cannot be refertilized or activated artificially.

6. Lack of development of the red halves obtained after fertilization is in striking contrast to the development of the red halves obtained before fertilization and subsequently activated artificially (parthenogenetic merogones).

7. Whole eggs may develop normally after centrifuging. They may separate later into 2 or 3 parts, forming nucleate red and white twins or triplets.