180 W. WALDEYER 
striction at the equatorial plane. For the process of division 
of the cell-body see below. 
Not until the cell has divided into two halves does the con- 
version of the daughter-skein into a resting daughter-nucleus 
commence. The first trace of a new nuclear membrane arises 
in the daughter-nucleus, distinctly before the commencement 
of cell-division, at the stage of the daughter-skein. Whence it 
arises is as little known as is the mode of disappearance of the 
mother nuclear membrane. According to Rabl, a daughter 
nuclear membrane is first seen at the antipolar side. The 
pole-bodies disappear with the commencement of the daughter- 
skein. Where the chromatic threads of the daughter skein 
touch they soon become branched and send out processes by 
means of which they unite with one another, so that later on 
a network of threads arises; they then lose their uniform 
thickness. Rabl is of opinion that certain thicker threads fuse 
by their limbs to form four longer threads, but denies, in agree- 
ment with his idea of the structure of the resting nucleus, that 
all thick threads unite with one another at their ends to form a 
single thread, so as to give rise to a single greatly wound 
daughter-thread, as Flemming, Retzius, and Heuser believe. 
Thus, a daughter “resting nucleus” succeeds the daughter- 
skein, which, together with its cell-protoplasm, has increased 
in size, and in all essentials resembles the resting mother- 
nucleus. As in the latter (cf. fig. 12) primary fibres, secondary 
fibres, pole-field, and antipole-field can be distinguished. The 
distinction between the two last regions is explicable, it is 
evident by the process of karyokinesis. As to when the 
nucleolus appears and how it arises, no concordant or satis- 
factory accounts have hitherto been given. 
If we collect all that is known at the present day about the 
process of karyokinesis, we shall be able to express its essential 
character most simply in the following words of Boveri (36) :— 
“The collection of the chromatic nuclear material in a (definite) 
number of isolated parts, of characteristic form, varying with 
the kind of cell—the chromatic elements; the forma- 
tion of an achromatic figure of threads, either from the nucleus 
