Nature of Formative Stimulation 131 



call forth the membrane formation not alone bv fattv acids 

 but by a number of different agencies and that all these means 

 act as formative stimuli. 



The causation of the membrane formation by a fatty acid 

 starts, therefore, the development in the sea-urchin egg, but 

 this development is abnormal and the egg is sickly and perishes 

 the more rapidly the higher the temperature. The question 

 arises, how can we inhibit this sickliness and grant a normal 

 development to the egg? 



I found that two different means are at our disposal for 

 this purpose. The one which never fails consists in putting 

 the eggs about twenty minutes after the artificial membrane 

 formation into hypertonic sea-water (or any other hypertonic 

 solution, e.g., sugar solution), i.e., into sea-water or any other 

 solution the osmotic pressure of which has been rendered 

 50 per cent higher than that of the sea- water. In this solution 

 the eggs remain from twenty to sixty minutes — according to 

 the temperature and the concentration of hydrox>'l-ions in the 

 solution. If after this time the eggs are transferred into normal 

 sea-water they develop at room temperature in a way similar to 

 the eggs which are fertilized by sperm. ^ 



The second method of causing the eggs to develop normally 

 at room temperature after the artificial causation of the mem- 

 brane formation consists in putting these eggs for three hours 

 in sea- water free from oxygen or into sea- water to which a 

 trace of KCN has been added. After the eggs are transferred 

 into normal sea-water they develop often but not always. This 

 method is, therefore, not quite as reliable as the other method 

 mentioned previously. 



We see, therefore, that the formative stimulus in the artificial 

 activation of the egg of the sea-urchin consists of two phases, 



1 The larvae originating from eggs fertilized by sperm live no longer tlian those 

 originating from eggs which develop parthenogenetically, if the larvae are not fed. 

 The feeding of these larvae is a tedious process and for this reason I have not 

 undertaken the task. Delage has, however, raised two such larvae until they were 

 sexually matvu-e. 



