264 W. WALDEYER. 
wigs), and in plants it occurs in the resting phase. The outward 
signs of the union must naturally be different according to the 
stage at which it occurs. A fusion of two nuclei to form one 
nuclear figure always occurs, even in Ascaris. Stras- 
burger therefore says (p. 230), “I should place the process of 
fertilization in the union of the threads of the sperm-nucleus 
and the egg-nucleus, but the further development of the 
‘segmentation nucleus’ depends on the mixing of the pro- 
ducts of the two nuclei. From the latter circumstance the 
copulation of the nuclear vesicles is easily explained, which is 
brought about in all objects in the most striking manner. The 
essence of the nucleus lies, however, in the nuclear threads, so 
that by the union of these a copulation of the nuclei is always 
brought about, even when the two nuclei, during the fusion, 
are no longer surrounded by a nuclear membrane. Therefore, 
in the future, the definition may well remain, that the essence 
of fertilization consists in the copulation of the sperm-nucleus 
and the egg-nucleus.”’ 
It is here impossible to quote all that Strasburger has 
brought forward in favour of this view. I must, however, 
refer to his important work, so frequently cited, on the process 
of fertilization in the Phanerogams, and ‘ Ueber Kern- und 
Zelltheilung in Pflanzenreiche’ (198, 191). I cannot, how- 
ever, satisfy myself as to the soundness of his arguments. He 
himself says that the essence of the nucleus lies in the nuclear- 
threads, and these nuclear threads do not fuse in Ascaris 
megalocephala. They certainly come close together tem- 
porarily in a division-figure, but this division-figure proves 
that there is no longer a simple fertilized egg-cell under obser- 
vation, but one in course of division in which already both 
division-poles are marked out. But we must place the act of 
fertilization before the commencement of segmentation. I 
therefore believe that we ought to adopt the views of EH. van 
Beneden and Kultschitzky in regard to the question of fusion. 
