INITIATION OF DEVELOPMENT IN THE EGG OF 



ARBACIA. 



I. EFFECT OF HYPERTONIC SEA-WATER IN PRODUCING MEM- 

 BRANE SEPARATION, CLEAVAGE, AND TOP-SWIMMING PLUTEI. 



E. E JUST,i 

 ROSENWALD FELLOW IN BIOLOGY, NATIONAL RESEARCH COUNCIL. 



It is well known from Morgan's work that unfertilized eggs of 

 Arbacia may be induced to develop through exposure to hypertonic 

 sea-water. Morgan, however, did not investigate the action of 

 hypertonic sea- water on the unfertilized egg much beyond its effect 

 in producing cleavage. Loeb extended these results of Morgan: 

 he was able by the use of hypertonic sea-water to produce plutei 

 from the unfertilized eggs of Arbacia. Two outstanding features 

 of Loeb's work strike the reader : first, he was not able with the 

 use of hypertonic sea-water to call forth " membrane formation " ; 

 nor was he able to obtain plutei of great viability, since these failed 

 to swim at the surface as do plutei from normally fertilized eggs. 



With his now classic method of exposing urchins' eggs to butyric 

 acid in sea-water before or after exposure to hypertonic sea- 

 water, Loeb was able to correct both these defects. On the basis 

 of these findings Loeb founded his famous lysin theory of fertili- 

 zation. He reasoned that butyric acid, as all haemolytic agents, 

 brings about a " superficial cytolysis " of the egg and thus the 

 formation of the " fertilization membrane." This " superficial 

 cytolysis," however, tends to be lethal and hence the egg must have 

 a corrective treatment to offset the initiation of death changes. 

 The hypertonic sea-water acts as this corrective factor. Accord- 

 ing to Loeb, it is of no moment whether he uses the corrective 

 agent first and follows with the cytolytic agent or vice versa. In 

 other words, the " uncorrected " egg may be first corrected, then 

 superficially cytolyzed ; or the egg may be first superficially cyto- 

 lyzed and saved from death by the corrective factor. In any 

 event, it is clear not only from Loeb's work, but that of others, 



1 Zoological Laboratory, Howard University. 



384 



