98 Artificial Parthenogenesis 



' In 1905 the writer found that membrane formation, 

 or rather the change of the surface of the egg under- 

 lying the membrane formation, is the essential feature 

 in the activation of the egg by a spermatozoon. He 

 observed that when unfertilized eggs of the Californian 

 sea urchin Strongylocentrotus purpuratus are put for 

 from one and a half to three minutes into a mixture of 

 50 c.c. of sea water+2.6 c.c. N/10 acetic or propionic 

 or butyric or valerianic acid and are then put into 

 normal sea water all or the majority of the eggs form 

 membranes; and that such eggs when the temperature 

 is very low will segment once or repeatedly and may 

 even — if the temperature is as low as 4°C. or less — 

 develop into swimming blastulae 1 ; but they will then 

 disintegrate. On the other hand, if they are kept at 

 room temperature they will develop only as far as the 

 aster formation and nuclear division and then begin 

 to disintegrate. It should be mentioned that the time 

 which elapses between artificial membrane formation 

 and nuclear division is greater than that between the 

 entrance of a spermatozoon and nuclear division. 



It was obvious, therefore, that artificial membrane 

 formation induced by butyric acid initiates the processes 

 underlying development of the egg but that for some 

 reason the egg is sickly and perishes rapidly. 



When, however, such eggs were given a short treat- 



1 The reader will find a description of the development of this egg in 

 the next chapter. 



