Cell division: direct measurement of maximum tension exerted by furrow of echinoderm eggs.

Tensions exerted by cleavage furrows in isometric contraction were measured by means of flexible glass needles whose characteristics of bending had already been determined. The tension of Astriclypeus manni furrows in second division is 3.04 x 10(-3) +/- 0.95 x 10(-3) dyne; that for Pseudocentrotus depressus eggs in first division is 2.00 X 10(-3) +/- 0.43 x 10(-3) dyne. The tension required for cleavage probably does not exceed 1.5 x 10(-3) dyne. According to existing morphological evidence, these values can be accounted for by a substance whose capacity for exerting tension does not exceed that of an actomyosin thread.