INTRODUCTION 



stages without it being necessary to expose them in addition to 

 hypertonic sea-water. At room temperature, on the other 

 hand, the eggs after artificial membrane formation go to pieces 

 in the course of a few hours. Hence it is the artificial membrane 

 formation which starts the development, but starts at the same 

 time a tendency to disintegration. The latter, however, can 

 be counteracted by a short exposure of the eggs to a hypertonic 

 solution; but in order to produce this effect the hypertonic 

 solution must contain a sufficient quantity of free oxygen, and 

 the higher the concentration of hydroxylions, within certain 

 limits, the more effective is the hypertonic solution. 



In 1906 I discovered still another method of overcoming the 

 injurious secondary effect connected with membrane formation, 

 which consists in arresting the development of the eggs for two 

 or three hours. This is effected by putting the eggs after mem- 

 brane formation into sea-water from which the oxygen has been 

 displaced by a current of hydrogen, or to which some KCN has 

 been added. As long as the eggs are in such a solution they 

 cannot develop on account of the cessation of their oxidations. 

 If the eggs are replaced some two or three hours later (at 15 C.) 

 in normal aerated sea-water, practically all the eggs segment 

 and develop in a perfectly normal manner. Hence there must 

 have occurred during that time a change in the egg which allows 

 it to develop normally. 



Further proof can be given that membrane formation is 

 really the essential step in the activation of development; 

 for in the eggs of many forms membrane formation is sufficient 

 to allow them to develop into normal larvae, at room tempera- 

 ture. I found that if membrane formation is produced in the 

 eggs of a starfish, Asterina, by the use of a fatty acid, some 

 of the eggs are able to develop into normal larvae; and I 

 afterward found the same to be the case with Polynoe, a poly- 

 chaet, while Lefevre established the same fact for the eggs of 

 another marine worm, Thalassema. Now these eggs differ from 



