184 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



from a theoretical point of view. The drawings in Figs. 54 

 to 58 depict the behavior of the unfertilized sea-urchin egg in 

 distilled water. It will be seen that during the first five minutes 

 the egg slowly but steadily increases in volume though its 



. 



Fig. 54 



Fig. 55 



Fig. 56 



Fig. 57 



Fig. 58 



FIGS. 54-58. Swelling and cytolysis of the sea-urchin egg in distilled 

 water. Slow but steady increase in volume of the egg in distilled water during 

 a period of five minutes (Figs. 54-57). Instantaneous membrane formation, 

 swelling and cytolysis of the egg within the sixth minute (Fig. 58). It is obvious 

 that the cytolysis is not caused by a bursting of the surface-layer of the egg. 



appearance remains the same (Figs. 55 to 57). Then it is 

 quite suddenly converted into a shadow within one minute 

 (Fig. 58); in that time it forms a membrane and swells enor- 

 mously. Hence a change of condition must occur in that 

 minute. At first the egg is in possession of a semi-permeable 

 membrane which is only permeable for water, but not for salts. 

 In this condition the changes noted in Figs. 54 to 57 occur. 



