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Toxopneustes

eggs, cleavage and concentration

TOXOPNEUSTES.

With the volume of sea-water and the concentration of sperm con stant, and with increasing numbers of eggs, a concentration was finally reached in which the rate of membrane formation, rate of cleavage, and total cleavage was considerably reduced.

In experiment 7/5 this injurious concentration was 1,084 eggs in 10 c.c. of sea-water in a Syracuse dish; 8,800 eggs in 7/8e; 9,120 eggs in 7/7e; 21,920 eggs in 7/13e; 38,400 eggs in 7/9e.

In a few experiments the injury was overcome in part by increasing the volume of sea-water 4 to 80 times; in most experiments the injury was not overcome in this manner. ( See 7/7B, 7/8B, 7/13c, 7/9B.) The decreased cleavage was due in part to insufficiency of sperm. The experiments to test this are in entire accord with those of Lillie. An increase of sperm increased cleavage 300 to 800 per cent. (See 7/8c, 7/9c, 7/13 D and E.) A decrease of sperm with low concentration of eggs did not affect the total cleavage. (See 7/13B.)

The lowered cleavage in high concentration of eggs was largely due to asphyxiation; this was evident in the experiments in which the high concentrations of eggs were gently shaken and the cleavage jumped from 0 or 1 per oent to 80 per cent. In other experiments when a few drops of highly concentrated suspension were removed to 10 c.c. of sea water, almost maximal cleavage occurred 15, 30, and 45 minutes after fertilization. ( See 7/14, B, c, D.) In Toxopneustes, therefore, optimum results were obtained when the egg concentration was below 8,000 in 10 c.c. of sea-water in a Syracuse dish and when fertilized by 1 drop of standard 0.05 per cent sperm suspension. In actual experimentation about one-tenth of this concentration of eggs was used, and in all experiments the sea-water was doubly filtered and stored in large quantities, to insure greater uniformity and to guard against evaporation.