THE BIOLOGY OF THE CELL SURFACE 



sometimes called the osmotic method for inducing develop- 

 ment of the unfertilized sea-urchin egg. 



This early work established that sea-water, if made suffi- 

 ciently hypertonic by the addition of electrolytes or non- 

 electrolytes, is capable of initiating development of 

 sea-urchin eggs. It shows that the effective agent is not 

 specific; the original failure to induce development with 

 the chlorides of sodium and potassium was obviously due 

 to an error which Loeb made in preparing the solutions. 

 It was soon learned that sea-water concentrated by boiling 

 is capable of inducing the development of this egg. I have 

 been able to induce experimental parthenogenesis simply 

 by allowing the eggs to remain uncovered in a glass dish 

 with sea-water; in this way, sufficient evaporation takes 

 place to bring the sea-water to that degree of hypertonicity 

 which is effective for stimulating the eggs to develop.^ 



But there are certain shortcomings to this osmotic 

 method. As we have seen, the eggs of sea-urchins separate 

 their vitelline membranes after insemination. The final 

 distance of the membrane from the egg and the rapidity of 

 this separation are indices of the physiological state of the 

 egg: an egg in best condition separates its membrane at a 

 uniform and rapid rate, with the result that it is equidistant 

 from the egg-surface at all points.- After the above men- 

 tioned treatment with hypertonic sea-water, sea-urchin 

 eggs do not show a separated membrane. Instead, the 

 vitelline membrane present on the egg before treatment 

 remains closely stuck; the hyaline plasma-layer beneath it 

 swells.^ Furthermore, the fertilized egg, if it be in opti- 

 mum condition, cleaves at a regular tempo and the blasto- 

 meres adhere to each other. After the treatment with 

 the hypertonic sea-water here discussed the blastomeres 



1 Just, igzSa. 

 - Just, igzSc. 

 ^ Just, 1919c, 1922b. 



220 



