FERTILIZATION 285 



fatty acid (butyric, propionic, or valerianic), and then back into pure 

 sea water: the membrane then forms by a cytolysis of the cortical layer 

 of the egg. Although in some forms (starfish) this one treatment is 

 sufficient to bring about successful development, in most cases (sea 

 urchin) the eggs become sickly and die. Loeb found that this sickli- 

 ness may be prevented, allowing normal development, by either of two 

 second treatments. If, after membrane formation, the eggs are placed 

 for 20 minutes in hypertonic sea water or other solution with an osmotic 

 pressure 50 per cent above that of ordinary sea water, they will develop 

 normally when returned to pure sea water. The same effect may be 

 brought about, though not always so successfully, by placing the eggs 

 for 3 hours in sea water free from oxygen, or into sea water with a trace 

 of KCN. It is therefore concluded by Loeb that the stimulus to such 

 parthenogenetic development has two phases: the inducement of mem- 

 brane formation by cytolysis, and the subsequent effect of the hyper- 

 tonic solution. In rare cases the first treatment alone is sufficient for 

 normal development, but in all cases it at least starts the egg into activity. 

 As a result of these experiments Loeb has interpreted the action of the 

 spermatozoon in normal fertilization on the assumption that it carries 

 two substances: first, a lysin which brings about membrane formation 

 by cytolysing the cortical layer of the egg, and which can act even if 

 the spermatozoon does not enter the egg; and second, a substance which 

 produces an effect similar to that of the hypertonic sea water employed 

 in the experiments. The quite different explanation offered by Lillie 

 will be mentioned further on. 



How it is that cytolysis of the cortical layer of the egg brings about 

 activation Loeb attempts to explain in the following manner. A calcium 

 lipoid compound forms a continuous layer just beneath the surface of the 

 egg, and the solution of this layer would probably result in the destruc- 

 tion of the cortical emulsion. It is assumed that in this cortical region 

 there is a catalytic agent which increases the metabolism (rate of oxida- 

 tion, etc.) of the egg. Following Warburg (1914) Loeb suggests that the 

 cytolysis releases the catalyzer by breaking down the cortical emulsion; 

 this results in an increase in the rate of oxidation and other reactions, and 

 development proceeds. 



That the process of activation is bound up primarily with reactions 

 occurring in the cortical region of the egg is shown further by the experi- 

 ments of Guyer (1907), Herlant (1913, 1917), McClendon (1912), Loeb 

 and Bancroft (1913), and particularly Bataillon (1910), who have shown 

 that the egg of the frog may be made to develop by pricking it with a 

 needle, especially if some blood enters the egg with it; and also by the 

 researches of R. S. Lillie (1908, 1915), who finds that starfish eggs may 

 be made to develop parthenogenetically by exposing them to high 

 temperatures for definite periods. (See F. R. Lillie, 1919, Chapter VII.) 



