1 64 PROBLEMS OF FERTILIZATION 



attained, or that the process of artificial activation, 

 unlike normal fertilization, is reversible. The first 

 . alternative runs counter to all the physiological deter- 

 minations, and the second is of so fundamental a character 

 that it requires most careful analysis. 



Loeb (1913) found that eggs of Strongylocentrotus 

 purpuratuSj in which membrane formation had been 

 induced by butyric acid, could be fertilized by sperm 

 if the membrane were torn by shaking; they differed 

 therefore in this respect from eggs in which membrane 

 formation had been induced by fertilization; but it is 

 noteworthy that such eggs differ from normally ferti- 

 lized eggs in requiring a second treatment after mem- 

 brane formation to induce development, so that the 

 activation by butyric acid is incomplete. Loeb (1913) 

 also determined that eggs of the same form when 

 treated with hypertonic sea- water alone might begin 

 development, but some of them come to a standstill 

 in the 2-, 4-, 8-, or i6-celled stage, and that such eggs 

 were fertilizable in the sense that insemination may cause 

 the formation of a separate membrane around each blas- 

 tomere; they then resume development in a perfectly 

 normal way, according to Loeb, and become normal 

 larvae. Here again fertilization is superimposed upon 

 incomplete parthenogenesis. Loeb concluded merely in 

 connection with these experiments that the block to 

 polyspermy is not due to the changes necessarily con- 

 nected with development. 



In later papers (19136 and 1915) he found that 

 alkalies induce development of eggs of Arbacia in a 

 manner somewhat similar to that of butyric acid; but 

 if the eggs after treatment for the proper length of time 



