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. 1 

 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- 

 besii 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 -f- 

 3 to 5 c.c. N/10 HC1 or HNO 3 ). 2 If the eggs were then 

 transferred to ordinary sea-water, some of them began to 

 develop into larvae. 



i R. 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. 



- Loeb and Neilson, P finger's Archiv, LXXXVII, 594, 1901; Untersuchungen, 



p. 278. 



