sions were united under the head of indirect or
mitotic divisions; these were also spoken of as karyo-kineses, and
were distinguished from the direct or amitotic divisions which are
characterised by a simple constriction of the nuclear body. So long
as the two kinds of indirect nuclear division were not clearly
distinguished, their correct interpretation was impossible. This was
accomplished after long and laborious research, which has recently
been carried out and with results which should, perhaps, be regarded as
provisional.

Soon after the new study of the nucleus began, investigators were struck
by the fact that the course of nuclear division in the mother-cells, or
more correctly in the grandmother-cells, of spores, pollen-grains, and
embryo-sacs of the more highly organised plants and in the spermatozoids
and eggs of the higher animals, exhibits similar phenomena, distinct
from those which occur in the somatic cells.

In the nuclei of all those cells which we may group together as
gonotokonts (At the suggestion of J.P. Lotsy in 1904.) (i.e. cells
concerned in reproduction) there are fewer chromosomes than in the
adjacent body-cells (somatic cells). It was noticed also that there is a
peculiarity characteristic of the gonotokonts, namely the occurrence of
two nuclear divisions rapidly succeeding one another. It was afterwards
recognised that in the first stage of nuclear division in
the gonotokonts the chromosomes unite in pairs: it is these
chromosome-pairs, and not the two longitudinal halves of single
chromosomes, which form the nuclear plate in the equatorial plane of
the nuclear spindle. It has been proposed to call these pairs gemini.
(J.E.S. Moore and A.L. Embleton, "Proc. Roy. Soc." London, Vol. LXXVII.
page 555, 1906; V. Gregoire, 1907.) In the course of this division
the spindle-fibrillae attach themselves to the gemini, i.e. to entire
chromosomes and direct them to the points where the new daughter-nuclei
are formed, that is to those positions towards which the longitudinal
halves of the chromosomes travel in ordinary nuclear divisions. It
is clear that in this way the number of chromosomes which the
daughter-nuclei contain, as the result of the first stage in division
in the gonotokonts, will be reduced by one half, while in ordinary
divisions the number of chromosomes always remains the same. The first
stage in the division of the nucleus in the gonotokonts has therefore
been termed the reduction di