1 68 DYNAMICS OF LIVING MATTER 



to swim, while those originating by the above-mentioned osmotic pro- 

 cess swim at the bottom of the dish. Fourth, the number of larvae 

 developing from fertilized eggs is, as a rule, practically 100 per cent, 

 while in the case of artificial parthenogenesis a much smaller percentage 

 of the eggs develop into swimming larvae. In the case of Arbacia, I 

 often succeeded in causing more than 20 per cent of the unfertilized 

 eggs to develop, but in the case of Strongylocentrotus - - the form of the 

 sea urchin common at Pacific Grove I was rarely able to obtain even 

 as high a percentage of developing eggs. Often enough only a fraction 

 of i per cent of the eggs yielded swimming larvae by the osmotic 

 method of artificial parthenogenesis. 



In thinking over the possible cause of this difference between the 

 development of the egg fertilized by sperm and of the egg caused to 

 develop by osmotic influences, it occurred to me that the spermatozoon 

 might carry into the egg not one, but several, substances or conditions, 

 each of which was responsible for only a part of the specific features of 

 sexual fertilization; and that in order to completely imitate the action 

 of the spermatozoon it might be necessary to combine two methods of 

 artificial parthenogenesis, each of which alone imitated the process of 

 sexual fertilization only partially. This latter idea proved correct far 

 beyond my expectations.* 



I found that if the eggs of Strongylocentrotus purpuratus are put into 



/yi 



50 c.c. sea water to which 3 c.c. - - of a fatty acid, e.g. formic, acetic, 



propionic, butyric or valerianic acid, are added, and are left in this 

 water for from one half to one and one half minutes, they form a mem- 

 brane when put back into normal sea water. The eggs go through the 

 internal changes characteristic of nuclear division, but they rarely seg- 

 ment. In about six hours they begin to disintegrate, and after twenty- 

 four hours scarcely an egg is left alive. If the eggs are left in the 

 acidulated sea water, they neither form a membrane nor segment. If 

 the eggs which have formed a membrane are put for from twenty-five 

 to fifty minutes into sea water whose concentration has been raised by 

 adding 15 c.c. 2\ n NaCl solution to 100 c.c. of sea water, the results 

 are surprising. Instead of a fraction of i per cent of the eggs develop- 

 ing, I had it in my power to cause 90 to 100 per cent of the eggs to 

 develop. All the eggs formed a membrane which is characteristic of the 

 egg fertilized with sperm. The rate of segmentation was practically the 

 same as that of the eggs of the same female fertilized with sperm. 

 A large percentage of the blastulae originating from this combination 

 of methods looked perfectly normal, and rose to the surface of the sea 



* Loeb, University of California Publications, Physiology, Vol. I, pp. 83, 89, 113, 1904. 



