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. 57 Fig. 58 
Fics. 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. AAt 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. 
