ARTIFICIAL PARTHENOGENESIS IN STARFISH 251 
they form beautiful membranes upon transference to ordinary 
sea-water. Butyric and caproic acids have a similar effect, 
while HCl and HNO, 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 fundamental 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 Californian 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 membrane 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. N/10 
butyric acid+50 c.c. of sea-water. In both lots all the eggs, 
except a few immature ones, formed a typical fertilization 
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 
