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~l;onverted 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. 



