168 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



normal sea-water after 180 minutes practically all disintegrated 

 into droplets and only a few developed. Not a single one of the 

 eggs which had been in the hypertonic solution in an atmosphere 

 of hydrogen developed when transferred to normal sea-water 

 after 128 and 180 minutes. The eggs appeared quite normal 

 and that they were really so is shown by the fact that they 

 developed normally upon the addition of sperm. 



In these experiments, of course, not all the oxygen had been 

 expelled from the hypertonic solution, but the pressure of the 

 oxygen had been depressed below the minimum necessary for 

 the developmental effect of the hypertonic solution. 



We will mention one further experiment. Unfertilized eggs 

 of a female were divided among five flasks, each of which con- 

 tained 50 c.c. of sea-water +8 c.c. 2J m NaCl. One flask was 

 left open, i.e., exposed to the air; the others, out of which the 

 air had been driven by passing hydrogen through them for two 

 hours, remained connected to the stream of hydrogen. After 

 2, 3, 4J, and 5J hours, one of the flasks was disconnected from 

 the hydrogen apparatus, and the eggs contained in it were 

 transferred to normal aerated sea-water. They were abso- 

 lutely unaltered and did not divide or develop. On the 

 addition of sperm 1 they all segmented and developed normally, 

 thus showing that they were really, not only apparently, 

 unchanged. Simultaneously a sample of the eggs from the 

 aerated hypertonic sea-water was also immediately transferred 

 to normal sea-water. The eggs transferred from this hyper- 

 tonic to normal sea-water after two hours yielded a good number 

 of normal blastulae. Only about 1 per cent of the eggs, trans- 

 ferred from the aerated hypertonic to normal sea-water after 

 three hours, developed; the rest disintegrated into small drops. 

 Those removed after 4J and 5| hours all went to pieces in the 

 same way. We can now understand another phenomenon 



1 The sperm should not be added until about an hour after the eggs are 

 replaced in oxygenated sea-water; otherwise the results are not so good. 



