KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 243 
changed into the achromatic threads of a nuclear spindle, 
whilst the chromatin spherules collect at its equator. At the 
same time, by division of the whole clear halo of the chromatic 
substance of the male nucleus, two male karyosomes are formed, 
which, however, do not at first share in the changes in the 
female karyosome. All that part arising from the protoplasm 
and paranuclei of the sperm mother-cell (“‘spermatide” of 
La Valette St. George), i.e. the tail and a small pale body 
between the head and the tail, will be cast off, and will gradually 
break down in the protoplasm of the egg-cell. Thus, the two 
male karyosomes arise only from the nuclear part of a 
spermatozoon. 
The pale substance of the male karyosome, also, probably 
become achromatic spindle-threads, while the chromatin spheres 
divide, so as to give eight spherules, which are united in 
couples to form double spheres. These eight (or if we reckon 
only the double spheres, four male chromatic elements) become 
associated with the female chromatin spheres, and all the 
chromatin spherules arrange themselves as an equatorial plate 
(Mutterstern) ; four spherules form one group. From sixteen 
to twenty such groups are present in the equatorial plate ; it is 
impossible to count them accurately. A fusion of male and 
female chromatin spherules is not proved. Platner says, on 
p. 67: “In Arion the two karyosomes arising from the head 
of a spermatozoon apparently arrive in the cavity of the egg- 
nucleus, but a fusion with its contents does not occur; rather 
the male and female nuclear portions separately take a share 
in the construction of the segmentation spindle.” Every group 
of four fuses into a larger chromatin spherule (chromosome). 
These chromosomes stretch along the spindle figure, and become 
converted into short rods; then follows Flemming’s typical 
longitudinal splitting of the chromosomes into two halves, 
which now, as in ordinary mitosis, separate towards the poles, 
in order to form the chromatin of the first two segmentation 
spheres. With regard to the question of fusion, Platner’s 
observations on Arion agree very well with those of van 
Beneden on Ascaris; but a striking difference is to be noted, 
