464 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



In the first experiment the alcohol-soluble phosphorus (phospho- 

 lipins) decreased by one-eighth, in the second by one-fourth, and this 

 decrease was progressive. The experimental evidence from a diversity 

 of forms therefore tends to establish a relationship between the disap- 

 pearance of lecithin or other phospholipins and the synthesis of nuclear 

 materials. 



This being the case, great importance attaches to the fact that 

 lecithin, when added to the medium in which sea-urchin embryos are 

 developing, strongly retards their development. The fertilization- 

 membrane is dissolved by lecithin, 1 and hence if lecithin in sufficient 

 concentration (0.15 per cent.) be added to sea- water containing recently 

 fertilized eggs, the membranes are disintegrated and the cleavage-cells 

 which have been formed fall apart, so that for merely mechanical 

 reasons further development is an impossibility. If more dilute leci- 

 thin solutions are employed this does not occur, but, at the same time, 

 no effect upon the rate of development is observed. Very different 

 results follow the exposure of the developing eggs to lecithin solutions, 

 however, after the fertilization-membrane has in the normal course of 

 development undergone rupture and liberated free-swimming blastulse. 

 The following experiment is illustrative of the phenomena which are 

 then observed: The eggs of a Strong ylocentrotus purpuratus female 

 were divided into two portions. Both portions were placed in sea- 

 water and fertilized with sperm. After twenty-four hours both lots 

 of eggs had developed into free-swimming blastulse. One portion was 

 now transferred to a mixture of fifty c.c. of sea- water and 5 c.c. of a 

 1.7 per cent, emulsion of egg-lecithin in sodium chloride solution 

 for a period of twenty-four 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. 



Days. Portion 1 (controls). Portion 2. 



1 Blastulse Blastulse (these were now trans- 



ferred to the lecithin mixture 

 for twenty-four hours). 



2 Gastrulae Blastulse (these were now trans- 



ferred to normal sea- water). 



3 . . . . . . Gastrulae Blastulse. 



4 . . . f . . . Gastrulse and early Blastulse. 



plutei 



5 '.'. . . Fully developed Blastulse and 25 per cent, gas- 



plutei trulse. 



6 Advanced plutei Early gastrulse with narrow 



unbranched intestine and 

 large clear body-cavity. 



7 . . . . Advanced plutei Unchanged. 



8 ... . . . Advanced plutei The gastrulse are now retrograd- 



ing; the intestine has almost 

 disappeared. 

 ' Unchanged Unchanged. 



1 We may infer from this that the periphery of the fertilization-membrane contains 

 hpoidal constituents which are essential to the integrity of its structure. 



