GERMINAL VESICLE AND FIRST EMBRYONIC NUCLEUS. 169 



constitution of the cell-nucleus in general, and the germinal 

 vesicle in particular, I thiuk it right to say that I do not in 

 the least coincide in this opinion of Auerbach and Hertwig. 

 A young nucleus is formed by a homogeneous substance 

 which 1 have called the nuclear essence.^ When this young 

 nucleus enlarges, the nuclear essence becomes united with a 

 substance which is taken up from the protoplasm of the 

 young cell. The nuclear substance which results from this 

 union forms the body of the nucleus. The membrane of 

 the nucleus, as well as the nucleoli, are the unmodified 

 remains of the primitive young nucleus ; they are formed 

 exclusively by the nuclear essence. At the moment 

 when a nucleus is about to divide the nucleoli as well 

 as the nuclear membrane dissolve in the nuclear sub- 

 stance. Hence it results that the contour of the nucleus 

 becomes scarcely distinguishable, and that the nucleoli dis- 

 appear. All who have studied the multiplication of cells 

 know how little the nucleus is apparent at the moment when 

 the division of the cell is about to take place. It is this fact 

 which has given rise to the theory according to which all cell- 

 multiplication is preceded by the disappearance of the nuclei. 

 The momentary disappearance and reappearance of the 

 nucleoli in the nucleus of the Gregarina were mentioned by 

 me in 1869. I was at that time unable to give any inter- 

 pretation of these facts ; still, they bear witness to the facility 

 with which the nucleolar substance dissolves in the nuclear 

 substance. The observations of which I shall give an account 

 later on, and which show that the spot of Wagner dissolves 

 in the germinal vesicle with the disappearance of the latter 

 element, form an argument which may be turned to account 

 in support of my opinion. Immediately after the dissolution 

 of the nucleoli and of the membrane in the nuclear substance, 

 a separation is effected between the nuclear essence which 

 goes to form the equatorial zone and the nuclear liquid which 

 is driven back to the poles of the nucleus. The latter, after 

 the division of the zone into two nuclear discs which are to 

 become new nuclei, loses itself in the body of the cell. 



The vacuoles which appear in so large a number of the 

 nucleoli are, I think, nothing but the result of the momentary 

 union of certain parts of the nucleolar substance with the 

 nuclear liquid. 



I believe that this way of looking at the constitution of the 

 nucleus is the only one which can explain the physical and 



' Edouard van Beneden, " Ue la Maturation de I'ceuf, de la Feconda- 

 tion et des Premieres Phenomenes du Developpement Embryonnaire des 

 Mammiferes," p. 50. 



