76 Wager and Penis ton.—Cytological Observations on 
the cytoplasm for special purposes, particularly in reproductive cells. But 
we know of very few cases in which the nucleus as such disappears, the 
nuclear network becoming dissolved in the cytoplasm, leaving only the 
nucleolus as the representative of the nucleus out of which new nuclei are 
to be developed (cf. Griggs, ' 09 ). 
Summary. 
A drawing of the yeast cell is here given (Text-figure), in which all the 
various structures described in this paper are diagrammatically represented. 
The nucleus consists of a nucleolus and a nuclear vacuole. The 
vacuole contains a clear nuclear sap, a peripheral network, and one or two, 
rarely more, bright refringent granules, which exhibit a Brownian move¬ 
ment. The nucleolus is attached laterally to the network, with which it 
Text-figure. Diagram of Yeast Cell. i. Nucleolus. 2. Peripheral layer of chromatin. 
3. Chromatin patch on one side of nucleolus. 4. Nuclear vacuole. 5. Central volutin granule in 
the vacuole. 6. Chromatin network. 7. Granules of fatty substance. 8. Volutin granules. 
9. Glycogen vacuoles. 10. Delicate suspending threads for the central volutin granule. 
is continuous, in such a way that a large part of its more or less spherical 
surface is in direct contact with the cytoplasm. There seems to be no 
definite limiting membrane around the nucleus, and the apparent disappear¬ 
ance of the vacuole in certain fixing fluids may be due to the contraction of 
the vacuole and the intrusion of the surrounding cytoplasm into it, in such 
a way that the delimitation between the two is no longer clearly visible. 
In its essentials the nucleus of the Yeast Plant possesses the normal 
structure of a nucleus, except that a well-marked nuclear membrane cannot 
be seen, and that the nucleolus is placed on one side of the chromatin 
network in direct contact with the cytoplasm. 
The nuclear vacuole varies much in size, according to the state of 
activity of the cell. At certain stages it becomes much contracted, and the 
