EGG SECRETIONS OF ARBACIA AND ASTERIAS 485 



A. Artificial activation 



In our attempts to understand activation, the method of 

 imitating the effect of sperm by physical and chemical means 

 has been of the greatest service. The first change to be noticed 

 when an echinoderm egg is fertilized is the appearance of a 

 'fertilization membrane.' Such membrane formation may be 

 brought about by a large number of agents (Loeb, '13, '16), 

 distilled water, the lower fatty acids, lipoid solvents, bases, 

 certain salts, increased temperature, shaking in some cases, 

 saponin, solanin, and bile salts. All of these cause cytolysis. 

 If the cytolysis is confined to the cortical layer of the egg, a 

 membrane will be formed and the egg will develop. Most of 

 these agents, however, if left to themselves, cytolyse not only 

 the cortical layer, but the whole egg. Loeb found it necessary, 

 therefore, either to follow the cytolytic agent with treatment 

 by hypertonic solutions in the presence of oxygen or to inhibit 

 oxidation. The latter may be accomplished by depriving the 

 eggs of oxygen or by treating them with a cyanide. 



So far as is known, there are only three classes of physiological 

 activators, the egg secretion of the same or related species, the 

 blood-serum of unrelated species, and, finally, the spermatozoon. 

 That the egg secretion may cause superficial cytolysis is indi- 

 cated by the work of Glaser, who found that it increases the 

 permeability of Arenicola larvae. Many investigators, notably 

 Friedenthal, have found that mammalian blood-serum contains 

 something which cytolyses cells of unrelated animals. Hence 

 it is not surprising to find that foreign blood and extracts of 

 foreign cells cause cytolysis and activation of Echinoderm eggs 

 (Loeb, '13). 



On the basis of these facts, Loeb ('12) concludes that ''the 

 spermatozoon, as well as the blood and tissues, contains a sub- 

 stance (lysin) which causes only cytolysis of the cortical layer." 

 Such a theory brings the phenomena of parthenogenesis and sperm 

 fertilization into one class. 



F. R. Lillie, on the other hand, believes that the spermatozoon 

 "functions essentially as the activator of a third body, 'ferti- 



