EFFECTS OF CENTRIFUGAL FORCE ON FERTILIZED EGGS OF ARBACIA PUNCTULATA AS OBSERVED WITH THE CENTRIFUGE-MICROSCOPE

¹ From the Marine Biological Laboratory, Woods Hole, Mass., and the Biology Department, Princeton University

1. Arbacia eggs centrifuged immediately (30-90 seconds) after fertilization become more elongate dumb-bells and break into halves and quarters more readily (most batches) than unfertilized eggs.

2. If centrifuged one and one-half to five minutes after fertilization, they break still more readily into many small pieces.

3. If centrifuged five to twenty minutes after fertilization (fertilization membranes previously removed), they form long streamers which break along their course. After twenty minutes, they elongate and break less and less readily. Treatment with calcium-free sea water makes them break more readily.

4. Some batches of eggs break more readily at every stage after fertilization than unfertilized eggs. Other batches break more readily only up to a certain stage, then less readily, the stage varying with different batches.

5. Fertilized eggs at all stages stratify less readily (that is, are more viscous) than unfertilized. The greater ease of breaking must therefore be due primarily to surface changes.

6. If centrifuged slowly while the fertilization membrane is being formed, this may be stretched and the egg pulled apart inside the membrane. The two parts may develop separately, either one or both according to the location of the sperm; or they may fuse together.

7. Parthenogenetic eggs at all stages up to cleavage act exactly like fertilized eggs.

8. Eggs may cleave even while being rotated at high speed (5000 times gravity); the cleavage plane passes through the oil cap and elongated axis of the cell.