Influence of Lecithin on Embryos. 



119 



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 de- 

 veloped into free-swimming blastulae. One portion was now trans- 

 ferred 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: 



Time After 



Fertilization. Portion i (Controls). Portion 2. 



1 day Blastulae. Blastulae. (These were now trans- 



ferred to the lecithin mixture for 24 

 hours.) 



2 days Gastrulae. Blastulae. (These were now trans- 



ferred to normal sea-water.) 



3 days Gastrulae. Blastulae. 



4 days Gastrulae and early plutei. Blastulae. 



5 days Fully developed plutei. Blastulae and 25 per cent, gastrulae. 



6 days Advanced plutei. Early gastrulae with narrow, un- 



branched intestine and large, clear body- 

 cavity. 



7 days Advanced plutei. Unchanged. 



8 days Advanced plutei. The gastrulae are now retrograding; 



the intestine has almost disappeared. 



9 days Unchanged. Unchanged. 



Bacterial invasion terminated the experiment after the 9th 

 day. It is evident that the immersion of blastulae 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 P er 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 



