STUDIES IN ARTIFICIAL PARTHENOGENESIS. 323 



showed small outbulgings which gave it a more or less crenate 

 appearance. Very soon, the membrane lifted away with con- 

 siderable rapidity. If success was to be obtained the egg had to 

 be removed from the solution at just about the time the crena- 

 tions appeared. 



As in Arbacia when the vitelline membrane is lifted from the 

 egg surface, a new membrane, no doubt a precipitation membrane, 

 is immediately formed about the egg cytoplasm. Sometimes it is 

 possible to cause this to become elevated also. Saponin produces 

 the best results. When eggs are exposed for 40 minutes to 0.2 

 per cent, saponin they are found to be surrounded by two 

 membranes. The outer one of these is quite far from the egg 

 and it was thought at first that it might represent the outer edge 

 of the jelly which had become visible. But this was shown not 

 to be true, for two membranes could be produced about eggs 

 from which the jelly had previously been shaken off. 



I have used the eggs of Cumingia for a number of years and in 

 some years I have found a tendency for a small per cent, of the 

 eggs to mature without apparently any treatment. In the experi- 

 ments recorded in this paper careful controls were always kept. 

 In every case at least two hundred eggs of the untreated- control 

 were examined for polar body formation. Of the experiments 

 cited in the table, in only one instance did the control show any 

 maturation. In the control for the ethyl nitrate experiment one 

 egg showed a polar body out of considerably over two hundred 

 examined. 



The table shows that eleven substances can produce polar 

 body formation and this is in every case preceeded by membrane 

 elevation. These eleven substances differ from each other very 

 widely in chemical constitution. It is almost inconceivable that 

 they should have any one chemical effect in common. Their 

 action must be primarily physical. It is believed to involve a 

 lowering of surface tension. The explanation which I have 

 offered for membrane elevation in Arbacia applies equally well 

 for Cumingia. For details of this explanation the reader is 

 referred to my earlier papers. 



Of course by choosing substances similar to those listed in the 

 table numerous other successful reagents could no doubt be 



