272 Dixon. — The Possible Function of 
sexual nuclei of sortie Ferns. A reference to Campbells 1 
and Shaw’s 2 figures will bear this out. 
It will thus be seen that if we do not assign hereditary 
functions to the nucleoli of the sexual nuclei we cannot in all 
cases assume the equivalence of the male and female hereditary 
masses. 
The view which has been just expressed with regard to the 
behaviour of the nuclear substances (chromatin and nucleoli) 
during karyokinesis, necessitates that Hertwig s second con- 
dition also should be fulfilled. The hereditary mass being 
composed of the nucleoli and chromatin is, according as it 
multiplies, equally distributed by karyokinesis among the 
cells derived from the fertilized ovum. 
We next come to the third condition laid down by Hertwig, 
which must be fulfilled by the hereditary substance. According 
to this, in order to prevent the summation of the hereditary 
masses resulting from the periodic fusions, there must be 
a corresponding periodic elimination of hereditary substance. 
Regarding the chromatin as the sole hereditary substance, 
investigators have believed that this elimination is effected by 
means of the so-called 4 division with reduction ’ which has 
been supposed to be of general occurrence during the formation 
of the sexual cells. During this division the chromosomes of 
the daughter-nuclei are supposed to arise by the transverse 
division of the chromosomes of the mother-nucleus, instead of 
by longitudinal division. In this manner half the number of 
idioblasts (hereditary units), which are supposed to be placed 
in series along the chromosomes, are distributed to one of the 
resulting nuclei and half to the other. 
The form of the chromosomes found in these divisions in 
animals appears to make it doubtful whether the cleavage of 
the chromosomes is longitudinal or transverse. The long 
chromosomes found in the karyokineses giving rise to the 
sexual nuclei of plants leave little room for such uncertainty, 
and all investigators, with one exception, are agreed that no 
1 Campbell, Messes and Ferns, Fig. 211. 
3 Shaw, Fertilization of Onoclea , Annals of Bot., Sept. 1898. 
