120 Artificial Parthenogenesis 



The idea that fertilization and membrane formation 

 cause an increase in the permeability of the egg was 

 later accepted and elaborated by R. Lillie. This 

 author assumes that the unfertilized egg cannot de- 

 velop because it contains too much C0 2 but that the 

 CO 2 can escape from the egg as soon as its permeability 

 is increased through the destruction of the cortical 

 layer of the egg. 1 After the C0 2 has escaped, the 

 excessive permeability must be restored to its normal 

 value and this is the r61e of the hypertonic treatment. 

 It is, however, difficult to harmonize the assumption 

 of an impermeability of the unfertilized egg for CO 2 

 with the fact that if the unfertilized sea-urchin egg is 

 cut into two, as is done in merogony, no development 

 takes place, while such pieces will develop when a 

 spermatozoon enters. The cortical layer is removed 

 along the cut surface and there is no reason why the 

 CO 2 should not escape. Besides, the experiments of 

 Godlewski and the writer prove that the cortical layer 

 of the unfertilized sea-urchin egg is apparently very 

 permeable for C0 2 since the latter causes membrane 

 formation if contained in the sea water in sufficiently 

 high concentration. 



Lillie assumes that the hypertonic treatment restores 

 the permeability raised to excess by the butyric acid 

 treatment, but this assumption is not in harmony with 



1 Lillie, R. S., Jour. Morphol., 1911, xxii., 695; Am. Jour. PhysioL, 

 1911, xxvii., 289. 



