ARTIFICIAL PARTHENOGENESIS IN STARFISH 253 
typical fertilization membrane. The length of exposure neces- 
sary for this was about 70 seconds at 35°, 40 to 50 seconds 
at 36°, about 30 seconds at 37°, and about 20 seconds at 38°. 
(These eggs can withstand a higher temperature than the 
eggs of S. purpuratus, which are killed too quickly at tem- 
peratures that induce membrane formation [34° to 35° C.] 
to be able to develop subsequently.) Lillie observed further 
that some of the starfish eggs, in which a membrane formation 
is produced by rise of temperature, develop without any further 
treatment. As in my experiments with Asterina, the time of 
membrane formation must be accurately chosen; for the time 
is not suitable unless the eggs are ready to give off the first polar 
body. 
But when Lillie put the eggs after artificial membrane forma- 
tion in sea-water to which enough KCN had been added to 
make it about a N/2,000 solution of KCN, many more eggs 
developed than in cases where this treatment was not used.! 
Now this is exactly the same result that I obtained with 
the eggs of sea-urchins after artificial membrane formation 
(see chap. ix). In this case the egg was given more time to 
produce the second factor before starting on its development 
and hence more eggs survived. 
3. My first experiments with starfish were carried out in 
1901, when Neilson and I found that the eggs of Asterias for- 
besiz could be made to develop when maturation had taken place 
by putting them for three to twenty minutes in sea-water to 
which some acid had been added (100 c.c. of sea-water-+ 
3 to 5c.c. N/10 HCl or HNO,).? If the eggs were then 
transferred to ordinary sea-water, some of them began to 
develop into larvae. 
1R. S. Lillie, ‘‘Momentary Elevation of Temperature as a Means of Produ- 
cing Artificial Parthenogenesis in Starfish Eggs and the Condition of Its Action,” 
Jour. Exper. Zool., V, 375, 1908. 
2 Loeb and Neilson, Pfliiger’s Archiv, LX X XVII, 594, 1901; Untersuchungen, 
p. 278. 
