AUTO-PARTHENOGENESIS IN ARBACIA AND ASTERIAS. 389 



ripe ovarian eggs, double their volume of sea-water. At the 

 end of ten minutes, during which the eggs were slightly agitated 

 at intervals, the suspension was centrifugated, and the eggs 

 cast down. After 100 revolutions the supernatant fluid was 

 carefully decanted and set aside for use. 



Ripe eggs were then shaken, usually from the ovaries of a 

 single individual, into a small quantity of fresh sea-water, and 

 to I c.c. of a concentrated suspension of these, was added i c.c. 

 of the secretion. In this mixture the eggs were allowed to stand 

 2 hours, when cleavages were usually found in all the dishes. 

 That these were not the result of accidental infection with sperm 

 was guaranteed by special precautions all dishes, instruments 

 and the hands as well as the animals used having been carefully 

 sterilized. Furthermore, when the first urchin opened was a 

 female, I usually sought no further, as the eggs from a single 

 individual are sufficient in number. Indeed in all but two or 

 three series only eggs from a single urchin were used. It might 

 be urged that the secretion or the sea- water were infected. 

 Sterilization of the latter however does not prevent auto-parthe- 

 nogenesis, and against the idea that the sperm might have been 

 present in the secretion there are three arguments, two of which 

 are conclusive. In the first place, as has been shown by F. R. 

 Lillie ('i3 2 ) and myself ('i4 2 ), the fertilizing power of sperm 

 decreases markedly if they are allowed to remain in the secretion 

 more than a few hours. In some of my experiments the secretion 

 was prepared a day in advance, and used on the eggs of the first 

 urchin opened on the following morning. In the second place 

 fertilization membranes never appeared in any of the experiments 

 with Arbacia eggs unless especially induced, and lastly, if the 

 same eggs from which the secretion was prepared were afterwards 

 subjected to its influence for the proper length of time and in 

 the proper concentration, characteristic auto-parthenogenesis 

 took place. 



Many experiments were tried varying the concentration of the 

 secretion as well as the time of exposure. My records indicate 

 cleavages at higher concentrations as well as lower, and also in 

 less than two hours, but the greatest number was always obtained 

 when i volume of the concentrated egg suspension was exposed 



