REVERSIBLE ACTIVATION AND INCOMPLETE MEM- 

 BRANE FORMATION OF THE UNFERTILIZED 

 EGGS OF THE SEA URCHIN. 1 



JACQUES LOEB. 



I. The writer showed in 1913 that the artificial activation of the 

 egg can be reversed under certain conditions. 2 When the egg 

 of Arbacia is treated with a base in the proper concentration 

 and for the proper length of time the effect is somewhat similar 

 to that which follows the treatment of the egg with a fatty acid. 

 The egg is induced to develop, it may segment (as a rule abnor- 

 mally) once or twice, and if nothing else happens it will perish 

 rather rapidly (unless the developmental processes are prevented). 

 If the eggs after the treatment with the acid or with the base 

 receive a treatment with a hypertonic solution of the proper 

 concentration and for the proper time they may develop into 

 larvae. 



The writer found that if the eggs are treated with alkali in the 

 proper way to induce development and if they are immediately 

 afterwards put for several hours into a solution which prevents 

 their development (sea-water with chloral hydrate or NaCN) 

 the eggs when taken out behave as if nothing had been done to 

 them. They neither segment nor do they disintegrate and they 

 can again be induced to develop by fertilization (or probably 

 with the methods of artificial parthenogenesis though the writer 

 has not yet tried this). The activating effect of the alkali is 

 therefore reversible. 



This reversibility is, however, only possible if the eggs have 

 not been exposed to the alkali too long. After too long an ex- 

 posure the effect of the alkali is no longer reversible by a tem- 

 porary suppression of the developmental processes. A second 

 condition for the reversibility is that the eggs are immediately 

 transferred from the alkaline solution into the chloral hydrate 



1 From the Rockefeller Institute for Medical Research, New York. 

 2 Loeb, Science, N. S. f XXXVIII., 749. iQU; Arch. f. Entwcklngsmech., 

 XXXVIII., 277, 1914. 



103 



