542 STUDIES IN GENERAL PHYSIOLOGY 



MgCl 2 with about 50 per cent, of sea- water was able to 

 bring about the same effect as the entrance of a sper- 

 matozoon. 1 The unfertilized eggs were left in such a solu- 

 tion for about two hours. When brought back into normal 

 sea-water they began to segment and form blastulse, gastrul, 

 and plutei, which were normal in every respect. The only 

 difference was that fewer eggs developed, and that their 

 development was slower than in the case of the normal 

 development of fertilized eggs. With each experiment a 

 series of control experiments was made to guard against the 

 possible presence of spermatozoa in the sea-water. Un- 

 fertilized eggs of the same female were brought into normal 

 sea- water, and in solutions with too little MgCl 2 . Neither 

 in the normal sea-water nor in any of these solutions with 

 too little MgCl 2 did one single egg develop into a blastula 

 or show anything more than the beginning of a segmenta- 

 tion after a long time. 



4. From these experiments it follows that the unfertilized 

 egg of the sea-urchin contains all the essential elements for 

 the production of a perfect pluteus. The only reason that 

 prevents the sea-urchin from developing parthenogenetically 

 under normal conditions is the constitution of the sea-water. 

 The latter either lacks the presence of a sufficient amount of 

 the ions that are necessary for the mechanics of cell-division 

 (Mg, K, HO, or others), or it contains too large a quantity 

 of ions that are unfavorable to this process (Ca, Na, or 

 others), or both. All the spermatozoon needs to carry into 

 the egg for the process of fertilization are ions to supple- 

 ment the lack of the one or counteract the effects of the 

 other class of ions in the sea-water, or both. The sper- 

 matozoon may, however, carry in addition a number of 



1 The subsequent experiments proved that the increase in the concentration of 

 the sea-water caused the development of the eggs. I was aware of this possibility 

 and was looking for it, but was misled through an error in the preparation of the 

 solutions (which I had intrusted to others). This error was afterward discovered 

 and corrected. [1903] 



