FERTILIZA TION 1 67 



to test the idea of the role of ion-proteids in the mechanism of living 

 matter. If it were true that the salts played the role which I was in- 

 clined to ascribe to them, it might also be possible to cause with their aid 

 the normal development of eggs. The experiments did not sustain this 

 idea as I had expected, but I succeeded in producing plutei from the 

 unfertilized egg of the sea urchin by exposing the eggs for about two 

 hours to sea water whose concentration had been raised by about 40 

 per cent to 50 per cent. It was immaterial which substance was used 

 to raise me concentration of the sea water, except for the fact that no 

 substances could be used which injured the eggs too much. The best 

 effects can be produced by raising the concentration of the sea water 

 through the addition of NaCl.* 



When unfertilized eggs are put into hypertonic sea water, they lose 

 water and shrink. When put back into normal sea water, they absorb 

 water again. We must therefore raise the question as to which of these 

 two conditions causes the egg to develop, the loss of water when the egg 

 is put into the concentrated sea water, or the taking up of water when 

 it is put back into normal sea water. It can be shown that the former 

 is the cause. If we increase the concentration of the sea water less 

 than 40 per cent, if e.g. we add 7 c.c. of a 2 J m solution of NaCl to 93 c.c. 

 of sea water, some of the unfertilized eggs of Arbacia will develop into 

 swimming blastula?, even if left permanently in the hypertonic sea water. 

 I have recently repeated this experiment with the eggs of Strongylocen- 

 trotus. If the eggs of this sea urchin were left in a mixture of 100 c.c. 

 sea water + 5 c.c. i\ n NaCl solution, after about six hours segmenta- 

 tion began, and after one or two days swimming larvae began to appear. 

 These larvae, however, did not develop into gastrulas or plutei, probably 

 on account of the abnormal condition of the sea water. In this case 

 only a loss, but no taking up, of water occurred. When the unfertilized 

 eggs of the sea urchin are put permanently or transitorily into sea water 

 which is diluted with distilled water, no development is produced. 



But although the osmotic method led to the development of larvae 

 from the egg, it differed in a number of points in its effects from the pro- 

 cess of fertilization by spermatozoa. In the first place, the eggs fertilized 

 with sperm form a characteristic membrane as soon as the spermatozoon 

 has entered, while the unfertilized eggs treated with hypertonic sea water 

 develop without the formation of a membrane. Second, the rate of 

 development is considerably faster in the fertilized egg than in the egg 

 caused to develop parthenogenetically. Third, the larvae originating 

 from fertilized eggs rise to the surface of the water as soon as they begin 



* Loeb, Am. Jour. Physiology, Vol. 3, p. 135, 1899; Vol. 3, p. 434, 1900; Vol. 4, 

 p. 178, 1900; and Science, Vol. 2, p. 612, April, 1900. 



