TRANSACTIONS OF SECTION K. 569 
the zygote of Pulyphagus euglene 1 have observed that a large portion of the 
nucleolar substance of both the sexual nuclei passes out into the cytoplasm, and 
there in some way assists in the preduction of the oily reserve substance which 
appears in it. It is also possible that, as Strasburger suggests, it may be con- 
cerned in some way in the formation of the nuclear spindle either by actually 
providing substance for its formation, or, what is perhaps more likely, by 
setting up certain changes in the cytoplasm which lead to its aggregation into 
fibrillee. 
Ifthe chromatic material of the nuclear network and nucleolus is the most 
highly organised of all the living constituents of the cell, it is probably intimately 
concerned in all the important activities of the cell, whether they lead to the 
storing up of reserve substances, or to the expression of the special activities of 
any particular cell, or to the production of those special modifications of the 
nucleus and cytoplasm by which the division of the cell is brought about. The 
function of the nucleolus may thus very well be simply that of a reserve of this 
highly complex chromatin which can be drawn upon as occasion requires. If we 
consider it in this light it will, I think, be found much easier to understand its 
relation to the complex changes which take place in the nucleus during 
division than if we regard it as a definite organ of the cell with a special function 
to perform. 
Division of the Nucleus in the Spore Mother-cells. 
The divisions of the nucleus which lead immediately to the formation of the 
spores possess some features which are not found in ordinary vegetative mitosis, 
' and which have an important bearing upon the facts of heredity. The first of 
these is known as the heterotype, the second as the homotype division. The 
essential features of the heterotypical division are as follows: The chromatin net 
becomes gradually resolved into a more or less continuous spireme. This thread 
(or threads) contracts into an irregular mass around the nucleolus, a phenomenon 
which was first discovered by Moore, and to which he gave the name of ‘ sinapsis.’ 
Some observers regard this contraction as caused by reagents; but since it bas been 
observed in the living condition by Miss Sargant and others, it is probably a defi- 
nite and normal stage in the division. It is concerned with some very pronounced 
changes which take place at thistime in the nucleus. The nuclear thread becomes 
more prominent, stains more deeply and exhibits a double row of granules which 
gives it the appearance of a double thread. This has been variously interpreted by 
different investigators: Miss Sargant, Farmer and Moore, and many others consider 
that it is due to a longitudinal splitting of the thread ; Dixon, Gregoire, Berghs, 
and Allen consider it as indicating a close approximation of separate loops of the 
thread. Whichever of these explanations is the correct one, the doubling gradually 
disappears and the thread becomes distributed through the nuclear cavity and again 
appears single ; it becomes shorter and thicker and once more becomes aggregated 
around the nucleolus. This may be, as Miss Sargant suggests, a second sinapsis. 
At this stage the chromosomes appear, but reduced to half the number of those which 
appeared in the previous divisions, so that they may be regarded as bivalent or 
double chromosomes. They become shorter and thicker, and gradually become 
grouped in the equatorial plane of the nucleus, where they become attached to the 
spindle fibres, Hach chromosome now divides into two halves, which pass to the 
respective poles of the spindle, to form, without the intervention of a complete 
resting stage, the division figures of the daughter-nuclei. 
The exact mode in which the division of the chromosomes into two halves 
takes place is the subject of much controversy. The studies of Weissman on 
the phenomena of heredity led him to the conclusion that the chromosomes consist 
of more than one complete ancestral germ-plasm, and that consequently these 
must be reduced in number in the sexual cells to escape the extraordinary com- 
plexity which would arise if the ancestral germ-plasms were doubled at each 
sexual fusion. As the longitudinal division of the chromosomes divides them into 
two equal halves it is qbvious that this will not reduce the number of ancestral 
