October 4, 1907] 



SCIENCE 



429 



Whenever we notice such an inconstancy 

 of results by a definite method it is prob- 

 able that some essential variable of the ex- 

 periment has been overlooked. It seemed 

 difficult to suggest what this variable 

 might be. But there was another chance 

 of overcoming this block. I had noticed in 

 my first experiments that the unfertilized 

 eggs which had been caused to develop 

 by the treatment with hypertonic sea- 

 water difilered typically in the form .of 

 their development from the eggs fertilized 

 by sperm. This fact was at first welcome 

 since it disposed of the general objection 

 that my results were due to an infection by 

 sperm. ■ The main differences were the fol- 

 lowing: the egg fertilized by sperm forms 

 immediately after the entrance of the 

 spermatozoon a fertilization membrane, 

 while in the egg caused to develop by the 

 osmotic treatment no membrane was 

 formed. It was also found that a segmen- 

 tation and development of the egg occurred 

 more rapidly and more regularly in the 

 fertilized egg than in the egg treated 

 osmotieally. These and other differences 

 led to the idea that the treatment of the egg 

 with hypertonic sea-water initiated only 

 certain, but not all of the developmental 

 effects of the spermatozoon. It therefore 

 seemed to be necessary to find a second 

 agency which in combination with the 

 osmotic treatment would allow a more com- 

 plete imitation of the effects of the sper- 

 matozoon. In the pursuit of this idea it was 

 found that if the unfertilized eggs of the 

 Californian sea-urchin, Strongylocentrotus 

 purpuratus, are treated for some minutes 

 with sea-water to which a small but definite 

 amount of a monobasic fatty acid (or any 

 acid with only one carboxyl group) was 

 added, they will form a typical membrane 

 of fertilization after being transferred to 

 normal sea-water. If these eggs are sub- 

 sequently treated for from 30 to 50 minutes 

 with hypertonic sea- water (50 c.c. sea- 



water plus 8 c.c. 2^iV NaCl) at a tempera- 

 ture of 15° C, practically all the eggs will 

 develop into larvae, provided the time of 

 exposure to the hypertonic sea-water is 

 correctly chosen. In a part of these eggs 

 the segmentation occurred in a perfectly 

 noimal way and these eggs developed into 

 normal plutei. If the eggs are treated with 

 only one of the two agencies, the fatty acid 

 or the hypertonic sea- water (for from 30 

 to 50 minutes) no egg develops. The call- 

 ing forth of the membrane formation alone 

 leads, at room temperature, to the forma- 

 tion of the first nuclear spindle and divi- 

 sion, and then soon to a rapid disintegra- 

 tion of the egg. The experiment can also 

 be made in the reverse order, namely, the 

 eggs can first be treated with the hyper- 

 tonic sea-water and then be submitted to 

 the treatment with fatty acid. If this 

 order is adopted the eggs must be exposed 

 to the hypertonic solution much longer 

 than in the other case, namely, for from 

 li to 2 hours. This difference in the dura- 

 tion of exposure is due tO' the fact that the 

 process of membrane formation leads to 

 an acceleration of certain chemical reac- 

 tions in the egg, whereby the hypertonic 

 sea-water can accomplish its effects more 

 quickly than if it is applied to an intact 

 egg. The superiority of this new method 

 of artificial parthenogenesis over the old 

 one is very striking in the eggs of 

 Strongylocentroius. It happened often 

 enough that the old, purely osmotic method 

 of artificial parthenogenesis led to the 

 formation of none or a small pei'centage of 

 larvaa, while the new method of combining 

 the fatty acid treatment with the osmotic 

 treatment led to the development of the 

 majority or practically all the eggs of the 

 same female. 



It could be shown that in this method we 

 are not dealing, with the direct effect of 

 the fatty acid upon the egg, but with the 

 effect of the membrane formation caused 



