KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 169 
that the network is denser near the periphery of the nucleus, 
and thus forms a perforated basket-like limiting layer. By 
others, an achromatic nuclear membrane is admitted for many 
nuclei, as, for instance, by Flemming (58) ; whilst many, like 
Strasburger and Pfitzner (154), believe in a membrane-like 
arrangement of the cell-protoplasm immediately around the 
nucleus—the “inner cell-membrane.” In his later contribu- 
tion (191, p. 30), Strasburger agrees with Guignard (84) that 
the whole nuclear membrane belongs genetically to the cell- 
protoplasm; it is a limiting layer of cell-protoplasm applied 
around the nuclear substance. At any rate it attains a 
more complete morphological individuality than the rest of 
the cell-protoplasm. It would certainly appear that the 
nuclear membrane belongs genetically to the cell-protoplasm, 
from the fact that in plant-cells it becomes associated with 
the protoplasm during karyokinesis, and becomes again arranged 
around the daughter nuclei. 
With regard to the chemical composition of the substance 
of the nucleus—an important item for a correct conception of 
the process of mitosis—recent researches have proved much, 
especially on the botanical side. Besides the “nuclein,” 
discovered by Miescher (137), which forms an essential part 
of the mass of the nucleus, Reinke and Rodewald (170) have 
found “ plastin,’ and Kossel (111—113) ‘“‘histon” and 
“adenin.” According to all present opinions, nuclein is found 
chiefly in the chromatic substance; see HE. Zacharias (208, 
209). Franz Schwarz (185) gives the following names to the 
various constituents of the cell-body and nucleus :—(1) “ Chro- 
matin,” which forms the substance of the Balbiani-Pfitzner 
chromatin bodies, of which a description has already been given. 
These are identical with Strasburger’s “ nucleo-microsomes,” 
a name which its author in his latest publication (191) gives 
up, on the ground that the chromatin bodies are chemically 
and morphologically different from the “microsomes” (‘‘ cyto- 
microsomes”), which must be regarded as the chief consti- 
tuents of the cell-protoplasm. (2) “ Linin” (dwvoy, thread). 
This substance is identical with Strasburger’s ‘“ nucleo-hyalo- 
