PAR THENOGENESIS 



are exposed to it. If we designate as optimum tlie short- 

 est exposures which are effective in calling forth complete 

 membrane-separation, we find, as my own experiments 

 have so clearly established, that sub-optimum exposures 

 instead of accelerating, actually retard the cytolysis which 

 in time normally takes place in sea-water.^ Eggs in sea- 

 water which show fully separated membranes in conse- 

 quence of optimum exposure to butyric acid cytolyze more 

 rapidly than unexposed eggs. Over-exposed eggs cytolyze 

 at a still more rapid rate. In his experiments Loeb never 

 used this reagent properly. That is, he exposed the eggs 

 of both the California and the Woods Hole sea-urchins 

 beyond the optimum time for membrane-separation. If 

 he had learned the best exposure, he probably would not 

 have so greatly emphasized in the butyric acid-hypertonic 

 sea-water method for the sea-urchin egg the cytolytic action 

 of the acid. Basing his theory on over-exposure to butyric 

 acid, he created the term, "superficial cytolysis."^ 



The superficial cytolysis-corrective-factor theory explains 

 the action of the two means for inducing parthenogenesis 

 as follows: the fatty acid treatment causes "superficial 

 cytolysis" and the hypertonic sea-water treatment follow- 

 ing "saves" the egg from this impending death. As I 

 stated above, the order in which the two agents are used is 

 of no consequence: the exposure of the eggs to butyric acid 

 may precede or follow that to hypertonic sea-water. That 

 is, the corrective factor (hypertonic sea-water), according 

 to the theory, if used first acts to correct where nothing is 

 to be corrected and the superficial cytolysis factor (the 

 fatty acid) used at the second place, tends to kill the more 

 than corrected egg. Thus the sequence in the treatment 

 so strongly demanded by the superficial-cytolysis-correc- 



^ Just, igzo. 



- See Just, ig/gc, 1920, ig22a, ig22b, igjoc. 



22g 



