SOME EFFECTS OF NUMBERS PRESENT ON THE RATE OF CLEAVAGE AND EARLY DEVELOPMENT IN ARBACIA

¹ From the Marine Biological Laboratory, Woods Hole, Mass.

1. Other conditions being equal and under a variety of experimental conditions, eggs of Arbacia punctulata cleave more rapidly when in relatively dense as opposed to relatively sparse populations. The decreased time to first cleavage in the dense populations was 0.88 minutes and to second cleavage was 2.23 minutes. The first difference is probably not statistically significant; the second value is clearly significant.

2. Among other conditions, these relations were observed when some thousands of eggs in a drop of 20 cu. mm. of sea water were connected by a narrow strait with a similar drop holding some few tens or even a few hundreds of eggs.

3. If the eggs were crowded together too densely, the time to first and second divisions was definitely retarded and the percentage of final cleavage was reduced.

4. When 22 to 56 eggs were placed in one drop of 20 cu. mm. connected by a strait with another containing 5 to 18 eggs, no difference in cleavage rate was observed.

5. The observed differences are not a result of differential temperatures externally imposed, differential hypertonicity or hypotonicity, contaminations with clomic fluid or with fragmented eggs.

6. Such results may be obtained by mass protection from toxic materials. There is, however, no indication that differences here reported were so caused.

7. Although no supporting evidence is presented here, the results may conceivably have been the result of differential temperatures produced by the high rate of oxidation of the massed eggs in a small space, by chemical emanations from the eggs, including carbon dioxide, by stimulation from mutual contact or by mitogenetic rays. Discussion of these problems is reserved for the present.

8. In addition to their intrinsic interest, the results provide another instance of physiological activities which proceed more rapidly at an intermediate optimum than when either too few or too many are present.