48 Wager and Penis ton.—Cy to logical Observations on 
of a cell under the microscope, he states that the vacuole rapidly contracts, 
and that the central moving granule which he regards as the nucleolus 
becomes lodged in one of the folds. 
Swellengrebel (’05) investigated nuclear division in compressed yeast. 
He describes the structure of the nucleus as similar to that given by Guil- 
liermond, but in opposition to Guilliermond he states that the nuclear 
division is mitotic. Four chromosomes are formed which arrange them¬ 
selves in the form of a band at the equator of a spindle-shaped figure. 
After probable division they separate into two daughter groups which 
pass to opposite poles, forming a diaster stage. This division com¬ 
mences before the cell buds, and the metaphase is reached before there is 
any sign of budding. The division appears to Swellengrebel to resemble 
that of the micro-nucleus in Paramoecium. 
Fuhrmann (’06) confirms in the main the results obtained by Swellen¬ 
grebel. The various stages of mitotic nuclear division were found, including 
the formation of four chromosomes, an achromatic spindle, and perhaps 
centrosomes. The resting nucleus is small, and in well differentiated pre¬ 
parations exhibits a delicate structure. The chromatic substance appears 
as an aggregation of fine granules, among which a larger granule is some¬ 
times seen, which may be a nucleolus. The presence of a nuclear membrane 
is by no means certain, and the clear space round the larger granule is 
nothing more than a vacuole either above it or below it. 
Kohl (’08) states that the nucleus consists of a distinct nuclear 
membrane, with nuclear sap, a large crystalloid, and a fine nuclear network. 
The figures given by the author seem to have been drawn from badly 
stained or over-stained specimens. The crystalloid is nothing more than 
the nucleolus, nucleus, or corpuscle of various authors. It appears to be 
homogeneous, and presents none of the characteristics of a nucleus ascribed 
to it by Guilliermond. The nuclear membrane which is figured around it 
probably represents the outline of the vacuole either above or below it, 
but no details are given as to the stage of development of the yeast from 
which the preparations were made. The author states that the nucleus 
divides by fragmentation both in budding and spore-formation. 
The conflicting accounts thus given by different observers are probably 
due not entirely to errors of observation, but to the remarkable variability 
in the behaviour of the nucleolus towards stains and reagents, to the varia¬ 
tion in the nuclear vacuole and its chromatin contents, and to the varying 
amounts of volutin, glycogen, and phosphorus found in the yeast at different 
stages in its development. These variations may be connected with the 
conditions under which the yeast cell lives, with its periods of great activity 
alternating with great depression in an environment which is constantly 
changing. How far this may be the case is, however, a question for further 
investigation. 
