ieee 
1887] The Significance of Sex. 145 
finally arrange themselves in the equator, so as to show in polar view as in , two of 
these loops were furnished by the male and two by the female. A side-view of this 
stage is shown in o, where the filaments have split in the middle, but not yet at the 
ends and the centre. In g the V-shaped loops have diverged towards the poles quite 
a ways; the central apices, however, move faster towards the poles than the outer 
limbs. hows the microsomata somewhat irregularly segregated at the base of a 
figure formed by the polar aster and spindle of conducting fibre, and at the apex of 
— the spindle of connecting fibrils, which is now constructing the cell-plate as ins. This 
e 
seems to show that the connecting fibres and the conducting fibres belong to distinct 
systems, which is more clearly shown in 7, where the karyosomata are placed at the 
ints of the meshes formed by the interlacing of the two systems. In the con- 
struction of the daughter-nucleus the microsomata pass by segmentation into a knauel 
like that seen in 7 and 4, and only when the equatorial plate is again formed for sub- 
sequent division do we get the four Ud once more established, as is seen respect- 
sg at the left and right of s. Van Beneden, however, ignores the evidence of his 
s, and states that the four loops remain distinct throughout. (See text for 
sibs prises n.) 
(c) KARYOKINESIS. 
WO extreme types of cell-division are known; in one, the 
nucleus simply constricts into two halves that move apart, 
followed by a similar constriction of the cell-body, so that each 
of the daughter-cells is provided with its own nucleus; in the 
other type the nucleus undergoes changes by which it becomes 
invisible to the microscope, unless the cell be treated with proper 
reagents, and as the partition which divides the cell-body appears, 
there is gradually built up a nucleus in each of the daughter-cells. 
The former type is known as direct division, the latter as indirect 
division. The term aryokinesis (nuclear motion) is usually re- 
stricted to the latter kind of division, but we are learning that 
there are many forms of indirect division that gradually unite the 
two extremes, so that we can no longer make the above dis- 
tinction. The term karyokinesis admits readily of a broad sig- 
nification, and we shall use the word as including all sorts of 
nuclear transformations 
Our knowledge of Gell stractuce and of the nucleus has won- 
derfully increased since 1833, when Robert Brown discovered the 
nucleus while studying the generative organs of orchids, and 
Von Mohi (1835) first saw it divide. To-day we are making as 
rapid progress in this direction as ever, and there is no field of 
biological research which offers so great inducements to the in- 
vestigator, or so valuable results as this. 
In all our progress there has been but one tendency, and that 
is to show us that the cell, and especially the nucleus, is a com- 
