WATER 



advantage of using eggs instead of other cells, especially 

 tissue-cells from a many-celled animal, lies in the fact that 

 one has more and sharper criteria for determining that the 

 cells are alive and normal. One very excellent criterion is 

 the fertilizability of the egg. Eggs that after return from 

 a hypotonic solution regain normal size, may sometimes 

 not be capable any more of fertilization or of develop- 

 ment. Or, as has happened in my studies, the hypotonic 

 sea-water induces parthenogenetic development. Fertili- 

 zation-capacity is then the best expression of normality. 

 If on return to normal sea-water the eggs not only regain 

 normal size but fertilize and develop as normally as eggs 

 that never had been in hypotonic sea-water, we may con- 

 clude that they have fully returned to normal condition. 

 In the table appended figures are given to show how far 

 eggs of Nereis recover after exposure to various degrees of 

 hypotonicity as measured by the per cent, of cleavage and 

 of swimming larvae. 



Table I. — Per Cent, of Cleavage and of Swimming Forms of Eggs 



Fertilized in Sea-water One Hour after Having Been Returned 



from Dilution of Sea-water, in Which They Had Been for 



One Hour* 



* This table represents one experiment of 10 made for each dilution. In most of the 60 experiments 

 the controls showed 100 per cent, cleavage and more than 90 per cent, normal trochophores. 



If one bars accidents and uses proper care to guard the 

 eggs against overcrowding and high temperature, they 

 develop as if never having been out of sea-water of normal 

 concentration. 



I2g 



