Abstract
When the eggs of Strongylocentrotus purpuratus are fertilized by sperm in a mixture of 50 c.c. of sea-water and 5 c.c. of a 1.7 per cent. suspension of lecithin in m/2 NaCl, the inner and outer fertilization-membranes are slowly dissolved by the lecithin, with the result that in the course of some six hours the cleavage-cells which have formed fall apart and ultimately disintegrate.
The eggs of Strongylocentrotus purpuratus female were divided into two portions. Both portions were placed in sea-water and fertilized with sperm. After 24 hours both lots of eggs had developed into free-swimming blastulæ. One portion was now transferred to a mixture of 50 c.c. of sea-water and 5 c.c. of a 1.7 per cent. suspension of lecithin in m/2 NaCl for a period of 24 hours and then returned to normal sea-water. The other portion was left in normal sea-water. The following table shows the relative development of the two portions:
Bacterial invasion terminated the experiment after the 9th day. It is evident that the immersion of blastulz for 24 hours in a 0.15 per cent solution of lecithin enormously retards their development.
If purpuratus eggs are fertilized by sperm in more dilute solutions of lecithin in sea-water (0.003 per cent. to 0.015 per cent.) the fertilization-membranes are not dissolved sufficiently rapidly to affect the development. In these solutions development is not appreciably retarded until the blastula stage is reached. There after development is very markedly retarded, and the retardation is greater the greater the concentration of the lecithin. The embryos are not injured by the lecithin, however, as they will ultimately develop to normal plutei if left in these solutions for a sufficient time.
If cholesterin, suspended in a mixture of m/100 sodium oleate and m/2 NaCl be mixed with the lecithin in equal proportions the retarding action of the lecithin upon the development of purpuratus eggs is almost completely neutralized.
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