Artificial Parthenogenesis in Starfish 251 



they form beautiful membranes upon transference to ordinary 

 sea-water. Butyric and caproic acids ha;ve a similar effect, 

 while HCl and HNO3 have much less or even no effect. 



When the eggs of Asterina are removed from the ovary, they 

 are, as we have seen, immature, i.e., they possess a large nucleus. 

 These eggs cannot be fertilized by sperm; it is also impossible 

 to produce membrane formation in such eggs by means of an 

 acid. Neither fertilization nor artificial membrane formation is 

 possible before the large nucleus has broken up and the extrusion 

 of the polar bodies has started. 



After artificial membrane formation, the starfish eggs begin 

 to divide. But in this they exhibit a fimdamental difference 

 in their behavior from sea-urchin eggs in which membrane 

 formation has been produced by a fatty acid. For whereas 

 at room temperature the eggs of the Cahfornian sea-urchin 

 begin to disintegrate after mere membrane formation — ^unless 

 they have been treated with hypertonic sea-water or with 

 KCN — the starfish egg is better off. For some of the starfish 

 eggs that have formed a meiribrane as a result of exposure to 

 butyric acid segment regularly and develop into normal larvae; 

 though the rest disintegrate, like sea-urchin eggs, after mem- 

 brane formation. In other words, the starfish eggs differ 

 from those of the sea-urchin in this, that they do not depend 

 upon the second corrective factor with the same degree of 

 necessity. 



In one experiment the eggs of an Asterina began to extrude 

 their polar bodies between 10 : 30 and 10 : 40. Some of the eggs 

 were then fertilized with sperm, while others were exposed for 

 one-half to one and a half minutes to the action of 6 c.c. N/10 

 butyric acid-|-50 c.c. of sea-water. In both lots all the eggs, 

 except a few immature ones, formed a typical fertihzation 

 membrane. In about two hours all the sperm-fertilized eggs 

 entered the two-cell stage, and at about the same time some 

 10 per cent of the eggs treated with butyric acid also began to 



