STUDIES IN ARTIFICIAL PARTHENOGENESIS. 337 



out that I have always realized the importance of cortical change. 

 On page 183 of my 1915 paper I stated in a section devoted to 

 the significance of cortical change, that "cortical change, whether 

 it be membrane swelling or elevation, always results in the re- 

 moval of this obstacle (i.e., a stiff membrane]. The vitelline 

 membrane is either rendered soft by swelling or it is lifted away 

 from the egg surface and its place taken by the no doubt less 

 rigid hyaline layer." I showed moreover that "at least two 

 processes which play a part in normal development would be 

 greatly hindered if some kind of cortical change did not occur." 



My results with Cumingia fully bear out this point of view. 

 Cortical change in Cumingia may take the form of a membrane 

 elevation dependent on a sharp decrease in surface tension. It 

 may more simply be just a membrane swelling. In both cases 

 the result is the same. The egg is freed from an obstacle which 

 impedes development. This in Cumingia as in Arbacia is the 

 restraining influence of a stiff vitelline membrane. In both eggs 

 the" same forces are involved in cortical change. The essential 

 features of the process and the effect on further development are 

 as closely alike as they could possibly be in the two cases. 



It should be noted that cortical change in Cumingia is not 

 ordinarily followed by segmentation. As in Arbacia cell-division 

 in Cumingia is preceded by a sharp increase in the viscosity of the 

 cytoplasm. This can be demonstrated by tests with the centri- 

 fuge. A number of such tests were made and the relation 

 established beyond a doubt. 



SUMMARY. 



1. The Cumingia egg is surrounded by a stiff vitelline mem- 

 brane which tightly encloses the fluid cytoplasm. 



2. A release from the restraint of this membrane is followed 

 by maturation. 



3. Such a release from restraint can be accomplished in three 

 ways; by membrane elevation, by membrane swelling, or by the 

 removal or rupture of the membrane. 



4. Substances which themselves have low surface tension pro- 

 duce a lowered surface tension of the membrane and this results 

 in its elevation from the egg surface. 



