Abstract
When unfertilized Arbacia eggs of one female were placed in the same hypotonic solution of sea water, at the same temperature and pH, the time required for 50% to cytolyze decreased sharply with ageing of eggs, i. e., the rate of cytolysis involving bursting of egg membranes increased rapidly with ageing of eggs.
Table I is an example of one experiment in which a 30% solution of sea water was used at 21.5° and pH 8.2. One hour after shedding, 50% burst in 14 1/2 minutes. When 73 hours old, 50% burst in 2 minutes.
Similar striking increase in the rate of cytolysis with ageing of eggs occurred in every experiment in every concentration, viz., o (distilled water), 10, 20, 30, 45, and 60% solutions of sea water.
The curves representing the rate of cytolysis in different concentrations of sea water were not parallel. In more concentrated solutions the initial rates of cytolysis were very much slower, but the final rates approximate closely the rates in more dilute solutions.
When eggs from one female were subjected at each age to 3 different concentrations, for example, 20, 30, and 45% solutions of sea water, at the same temperature and pH, the 3 curves representing the rates of cytolysis in each solution converged with ageing of eggs. The terminal rates are closely correlated with the osmotic pressure differences across the egg membrane. The convergence indicates a greater effect of osmotic forces on cytolysis at later ages and, conversely, lesser effect at early ages.
The increase in surface area of eggs placed in a given hypotonic solution at constant temperature and duration, is greater with ageing of eggs. This is due to increased permeability of the egg membrane with age.
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