PAR THENOGENESIS 



especially on that of Jstropecten, one is struck more by his 

 failures than his success to obtain parthenogenesis.^ Were 

 the eggs of these two starfishes normally parthenogenetic, 

 he would have secured a higher per cent, of development; 

 also, the development would have gone farther and would 

 have more closely resembled that of fertilized eggs. Three 

 years earlier, when he attempted to observe parthenogenesis 

 in the eggs of Asterias and so to repeat Greef's work, he 

 had either changed or aerated the sea-water, so that the 

 sea-water neither increased in hypertonicity nor in tempera- 

 ture and did not become charged with carbon-dioxide. 

 At that time he failed completely to secure development 

 beyond the establishment of the definite egg-nucleus. In 

 other words, the eggs, as is normal for them, merely com- 

 pleted maturation in sea-water. In the later experiments 

 where he observed parthenogenetic development, he does 

 not mention having protected the eggs against changes in 

 the sea-water. The one egg that reached the blastula- 

 stage, though seemingly normal in outward appearance, 

 lacked the separated membrane so characteristic of the 

 fertilized egg and of that which has been induced to develop 

 by means of treatment with CO2 or with increased tempera- 

 ture. This observation on the single blastula obtained, 

 strongly indicates in the light of my experience that Hert- 

 wig induced parthenogenesis by means of sea-water made 

 hypertonic through evaporation. 



The strongest evidence that both Greef and Hertwig 

 induced parthenogenesis experimentally in these eggs lies 

 in the fact that although starfish eggs are extremely 

 responsive to experimental means, no one since has suc- 

 ceeded in demonstrating that they are normally partheno- 

 genetic. My experience with the egg of Astropecten 



^ Hertwig, 0., iSgo. 



215 



