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

Abstract

Other conditions being equal and under a variety of exp. conditions, eggs of A. punctulata cleave more rapidly when in dense as opposed to sparse populations. The decreased time to 1st cleavage in the dense populations was 0.88 minutes and to 2d cleavage was 2.23 min. The second value is clearly significant statistically. Among other conditions, these relations were observed when some few thousands of eggs in a drop of 20 cu. mm. of sea water were connected by a narrow strait with a similar drop holding a few tens or even a few hundreds of eggs. If the eggs were too crowded, the time to 1st and 2d cleavages was retarded and the % of final cleavage was reduced. When 22 to 56 eggs were placed in one drop of 20 cu. mm. connected by a strait with another containing 5-18 eggs, no difference in cleavage rate was observed. The observed differences are not a result of differential temps. externally imposed, differential hypertonicity or hypo-tonicity, contaminations with coelomic fluid or with fragmented eggs. Such results can be obtained by mass protection from toxic materials; however, there is no evidence that the differences here reported were so caused. Discussion of causal factors is reserved.