>. 
vanishes. Î came to the same conclusion with Closterium !), 
in which Lauterborn *) had described a ring-shaped 
nuclear-plate. 
The nuclear-plate divides by longitudinal splitting into 
two halves which separate (Fig. 8 and 9). At first their 
structure becomes more dense. When, by the use of 
chromic acid, they have been isolated and fall over, they 
somewhat resemble round discs which appear spotted in 
consequence of local differences in density. These halves 
of the nuclear-plate develop into daughter-nuclei which 
acquire a membrane and consequently show a sharp 
outline (Fig. 10). It is difficult to say when the nuclear 
membrane reappears. The dense structure of the halves 
of the nuclear plate again gives place to a looser one 
and finally there is again spread out within the nuclear- 
membrane a fine network, which resembles that of the 
resting nucleus. During the entire process of karyokinesis 
the nuclear network forms a coherent whole. When the 
structure becomes looser again, the nucleoli also quickly 
appear. At first there can be distinguished in the network 
many small masses more or less globular and irregular, 
which gradually unite into several larger masses (Fig. 10) 
and finally form one single spherical mass in the centre 
of the nucleus. This representation of the origin of the 
nucleolus differs very much from that given by Escoyez, 
but it agrees with what has been observed in Spirogyra 
where also many nucleoli flow together into a single one. 
There is a further point to be noted concerning the 
development and position of the daughter nuclei in Zyg- 
nema cruciatum. In Spirogyra and other cases the halves 
of the nuclear plate take up a position near the poles of 
1) C. van Wisselingh, Ueber Kernstruktur und Kernteilung bei 
Closterium, Beih. zum Bot. Centralbl., Bd. XXIV (1912), Abt. I. p. 429. 
?) R. Lauterborn, Untersuchungen über Bau, Kernteilung und Bewe- 
gung der Diafomeen, 1896, Fig. 68. 
