i62 PROBLEMS OF FERTILIZATION 



The mechanism for the prevention of polyspermy 

 must operate at an exceedingly high rate of speed; 

 this is readily appreciated when we consider that it 

 is effective in selecting only one out of the many sper- 

 matozoa that appear to the eye to reach the ovum 

 simultaneously. It must therefore be effective before 

 the fertilization membrane forms, so that it becomes 

 somewhat superfluous to inquire whether this mem- 

 brane furnishes an unnecessary further protection. 

 This subject is discussed further in chapter vii. 



An excellent method for experimental investigation 

 of this problem was discovered by 0. and R. Her twig 

 (1887), who found that when sea urchin eggs are broken 

 into fragments the non-nucleated fragments may be 

 fertilized no less than the nucleated fragments, a phe- 

 nomenon that subsequently became known as me- 

 rogony. Boveri (1889), Morgan (1895), ^^d Seeliger 

 (1894-96) utilized this method for study of the problem 

 of nuclear transmission of hereditary qualities; Driesch 

 and others for problems of physiology of development; 

 and the method was subsequently used for testing the 

 changes in the cytoplasm of the egg with reference to 

 fertilizability. 



The classic experiments along the latter lines are 

 those of Delage (1898, 1899, 1901) and of E. B. Wilson 

 (1903). Delage's observations included sea urchins, 

 starfish, an annelid (Lanicc), and a mollusk {Dentalium). 

 Fragments taken from eggs with intact germinal vesicle 

 are unfertilizable; but fragments taken from eggs in 

 which the germinal vesicle has begun to break down 

 may fertilize, and after complete dissolution of the 

 germinal vesicle fragments are completely fertilizable. 



