28 RALPH S. LILLIE 



is indispensable to the production of a large proportion of larvae ; 

 if this treatment is omitted the vast majority of eggs invariably 

 undergo cytolysis. 



These conditions suggest that in the sea-urchin egg the cytoly- 

 sis following simple membrane-formation is an expression of the 

 undue persistence of a condition of increased permeability; and 

 that the after-treatment serves essentially to bring the permea- 

 bility again to the norm." In the normal egg a curve of polar- 

 ization-change (dependent on permeability-change) of the 

 following general form probably follows the entrance of the sper- 

 matozoon; there is an initial depolarization resulting from the 

 increase of permeability, and lasting for perhaps fifteen minutes ; 

 following this the permeability and the correlative polarization 

 return to or toward the original condition, where they remain 

 unchanged until the period of the first cleavage, when a second 

 temporary depolarization takes place; a similar change recurs 

 with each succeeding cleavage. In parthenogenetic fertiliza- 

 tion with a cytolytic agent it is to be assumed that the initial 

 treatment also causes an increase of permeability with accom- 

 panying depolarization, from which however the egg recovers 

 only imperfectly unless subjected to a second treatment whose 

 general effect on permeability is of the reverse kind, that is, of a 

 kind tending to restore the original semi-permeability of the 

 membrane. On this hypothesis the beneficial effect of the after- 

 treatment depends on what may be broadly characterized as an 

 anti-cytolytic action. The total process thus consists in a pre- 

 liminary permeability-increasing treatment — equivalent to cy- 

 tolytic if the condition is not soon reversed — followed after the 

 proper interval by one whose general effect is permeability-de- 

 creasing or anti-cytolytic. If this is true it ought to be pos- 

 sible to substitute for the after exposure to hypertonic sea water 

 or other favorable condition a treatment with other substances 

 or agencies whose general effect is to decrease the permeability 

 of the plasma membrane or to oppose any further 'increase 

 of permeability. Such treatment ought to check or prevent 

 the progressive breakdown or cytolysis otherwise following the 



1^ Cf. R. S. Lillie, American Journal of Physiology, 1911, vol. 28, p. 285; Godlew- 

 ski, Archiv fiir Entwicklungsmechanik, 1911, vol. 33, p. 225. 



