The Essence of Fertilization 227 



enough to be discernible with the naked eye, the cyto- 

 plasm with all its cilia remains in the outer layers of the 

 egg-cell, while only the nucleus penetrates more deeply. 

 The beautiful investigations of Webber and Ikeno have 

 brought this process to light. 



Finally the two nuclei come into contact and unite into 

 a single body. This is the most important moment of 

 fertilization, the whole physiological process is concluded 

 by this union. 



Let us ask now what has been achieved by it. Appar- 

 ently very little, for the two parental nuclei are only 

 closely appressed to each other. A penetration or fusion 

 of their substance does not take place. They remain sep- 

 arate in spite of the union. With fertilization the life of 

 the new germ begins, and in most cases immediately. 

 Originally a single cell, the germ soon divides into two 

 and then into more cells. But this beginning of the vege- 

 tative life takes place everywhere before the two parental 

 nuclei have entered into closer union. Only after the 

 first division does the limit become unrecognizable, the 

 contact of the constituent parts of the male and female 

 halves being now so intimate that there is at least the 

 appearance of a fusion. 



It was the Belgian investigator, van Beneden, who dis- 

 covered this all-controlling fact. He first observed the 

 independence of the paternal and the maternal nuclei 

 in the intestinal worm, Ascaris, then elsewhere in the ani- 

 mal kingdom, and immediately recognized its significance. 

 Since life could begin without fusion of the two nuclei, 

 he considered that such a thing was not necessary, and 

 assumed that all through life the two nuclei preserve their 

 independence more or less completely. 



According to this view the nuclei are double beings, 



