THE BIOLOGY OF THE CELL SURFACE 



eggs are in a bad condition brought about by the injurious 

 action of the agent employed to remove the jelly. ^ The 

 physiological condition of all eggs known to me can be 

 impaired by exposure to low temperatures. Indeed, since 

 low temperature (like high) is an experimental means, to 

 experiment on eggs from animals which have been kept in 

 the ice-chest in order to delay shedding, is equivalent to 

 compounding experimental procedures whose effects may 

 be complementary or antagonistic. Thus, I would never 

 think of exposing eggs of Platyniereis, for example, which 

 had been kept over night in the cold room (at 5°C.) to 

 ultraviolet light because the low temperature alone gives 

 the eflFect of polyploidy to obtain which I use the ultra- 

 violet radiation.^ 



From a series of experiments made on the capacity of a 

 sea-urchin's eggs to develop without spermatozoa, it was 

 concluded that development can be caused by immersing 

 the eggs in sea-water which had been charged with a sub- 

 stance liberated by others of the same species. This con- 

 clusion was unwarranted because, as I found, the results 

 obtained are solely due to evaporation of the sea-water 

 and not to the presence of substances originating from the 

 eggs.^ Another series of experiments was used to prove 

 that this subtance liberated by the eggs and held to be the 

 cause of their development, had been isolated. But I 

 found that sea-water treated by one or by all of the reagents 

 employed for precipitating the alleged substance was if 

 anything more effective for causing development than 

 sea-water containing the egg-substance. Thus the develop- 

 ment was due not to the isolated (precipitated) sub- 



^ For discussion of this subject, see Just, ig2Sc. Derbes, 184"/ 

 knew not only that jelly surrounds the sea-urchin's egg but also that 

 its absence does not impair the egg's development. 



~ Just, ig2()e. 



2 Just, igzSa. 



20 



