188 Mother.—Nttclear and Cell Division 
are justified in attributing to the centrosome the morphological 
rank of an organ, such as the nucleus. It is, it seems to me, 
more in harmony with all facts pertaining to the subject to 
regard the centrosome as a special individualized part of the 
kinoplasm, existing in that form as the expression of certain 
activities which are as yet not well understood. 
In comparing the development of the spindle in Dictyota 
with that of Stypocaulon , a close resemblance of the two is 
at once apparent. From each pole or centrosome kino- 
plasmic fibres enter the nuclear cavity. The membrane of 
the nucleus is unbroken at first, but later it gradually dis¬ 
appears at the poles. The remaining part of the membrane 
persists until a very late stage, sometimes after the spindle 
is mature. 
The entering cones of spindle-fibres present less regular 
and even bases than those in Stypocaulon , a fact due to the 
more rapid growth of certain fibres. These cones meet in 
the equatorial region to form that part of the spindle between 
the poles. By this process the chromosomes are brought 
into the equatorial plate. 
During the prophase of both divisions in the tetraspore 
mother-cell the behaviour of the chromatin differs strikingly 
from that in the higher plants. There is not developed here 
a regular and continuous chromatin-spirem which segments 
into the chromosomes, but these arise as isolated masses, 
often differing much in size. It gives the impression that the 
quantity of chromatin is not sufficient to form a continuous 
spirem. In the vegetative cells, on the contrary, there is 
developed a typical spirem as in the higher plants. 
The reduced number of chromosomes, namely sixteen, 
appears in the first nuclear division in the tetraspore mother- 
cell. This division is quite analogous to the heterotypic 
division in spore mother-cells of most cormophytes. In the 
vegetative cells of the thallus bearing tetraspores the number 
is estimated at thirty-two. 
The behaviour of the nucleolus, during both the develop¬ 
ment of the nuclear figure and the construction of the daughter 
