THE ORGANIC CELL 
48 
and cytoplasm. This fundamental process of cell-division is 
characteristic of all living forms, and from this fact alone it 
is evidently a phenomenon of the most profound importance. 
This radical difference between cytoplasmic and nuclear 
division, by which in the case of the nucleus the chromatin 
is passed on from the mother-cell to its progeny, leads one 
irresistibly to the only logical conclusion — that chromatin 
is the physical basis of heredity. 
The Nucleus in Fertilisation. 
The facts derived from the process of fertilisation lend 
a weight to the argument in favour of the nucleus which is 
overwhelming. As is well known, the ovum supplies practically 
all the cytoplasm for the embryonic body, the amount derived 
from the spermatozoon being infinitesimal, and yet the influence 
of the sperm on the offspring is quite as great as that of the 
ovum. 
The chromatin of the germ-nuclei is divided with absolute 
equality between the first two, and very probably to all the 
later-developed cells. That this equal division of the chromatin 
among all later-formed cells is practically a certainty must be 
conceded from the experiments of Riickert and others described 
elsewhere. It is therefore evident that the character of the 
cell is the result of nuclear action, and that on account of the 
equal distribution of the maternal and paternal chromatin 
to every cell descended from the original germ-nuclei we get 
an insight into the remarkable fact that every part of the 
offspring may be like either or both parents. 
Boveri performed a series of brilliant experiments with 
the eggs of two different species of sea-urchins, Echinus micro- 
tuberculatus and Sphcerechinus granularis, which are very 
common in the Bay of Naples. If the minute eggs of either 
of these species are violently shaken with a little sea-water 
in a suitable vessel, they break up into various-sized fragments, 
some of which contain nuclei, others not. Boveri found that 
these fragments, if fertilised, developed into normal larvae. 
The non-nucleated as well as the nucleated portions developed 
in the usual manner, the spermatozoa entering both with 
