XXXII 



FURTHER EXPERIMENTS ON ARTIFICIAL PARTHENO- 

 GENESIS AND THE NATURE OF THE PROCESS OF 

 FERTILIZATION ' 



1. IN my previous communications on the subject of arti- 

 ficial parthenogenesis 2 I had confined myself to the proof of 

 the fact that the unfertilized eggs of Arbacia and Strongy- 

 locentrotus franciscanus and purpuratus, are capable of a 

 development into the pluteus form if kept for from one to 

 two hours in a mixture of equal parts of a 2 -^ n MgCl 2 solu- 

 tion and sea-water. The above-mentioned solution, which 

 brings about the artificial development of the egg, differs in 

 three directions from the constitution of the normal sea- 

 water. First, the osmotic pressure of the solution is higher 

 than that of the normal sea-water ; second, one-half of the 

 salts contained in normal sea-water are removed. It might 

 be possible that the sea-water contains ions which are in- 

 jurious to the development, and that the removal of these 

 ions makes the development of the unfertilized eggs possible. 

 Third, a considerable amount of MgCl 2 is brought into solu- 

 tion, and it might be that the Mg ions have a specific "stimu- 

 lating" effect upon the development. For the determination 

 of the nature of the process of fertilization it was necessary 

 to find out which of the three conditions is essential for the 

 production of artificial parthenogenesis. 



2. I had already mentioned in a previous paper that the 

 mere change in the constitution of the sea-water, if not 

 accompanied by an increase in its osmotic pressure, can only 



1 American Journal of Physiology, Vol. IV (August 1, 1900), p. 178. These ex- 

 periments were carried out with the aid of the Elizabeth Thompson Science Fund. 



2 Part II, pp. 539, 576, and 624. 



638 



