698 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
I. Formation of Polar Globules. — The emission of polar globules 
seems to be always associated with true karyokinetic division, that is, 
the chromosomes that are present are always divided in the formation of 
every polar globule, and the halves shared between the two daughter-cells. 
When the chromosomes are rod-like or iilamentar, cleavage takes place 
in a longitudinal direction. In one and the same ovum the two polar 
spindles have the same number of chromosomes. The so-called matura- 
tion of the ovum presents us with a case in which the fate of the several 
chromosomes may be followed out during the whole course of the existence 
of a cell — the mother egg-cell. The fact that the chromosomes which 
are present in the division of this cell are identical with those which the 
cell had at its formation, induces us to conclude that the same is the case 
with those cells where the fate of the several elements has escaped ob- 
servation. A peculiarity which may often be observed in the chromatic 
elements of the first polar spindle is that there are four of them. On 
this point the author dilates at some length. The elements emitted in 
the two polar bodies are, to our eyes, exactly identical with those which 
remain in the egg. In such eggs as have the polar spindles composed 
of two “ ray-suns ” the poles of the second spindle arise by division of 
the pole of the first, which remains in the egg. 
II. Fertilization. — There is a certain variability in the relation of 
the chromatic substance in fertilization. The most striking point at 
first sight is the fact that in some cases the egg- and sperm-nuclei fuse, 
while in others they divide independently and break up in the fusing. 
The former has, up till now, been erroneously regarded as the more 
common process. As these differences have been observed in the several 
nuclei of eggs of one and the same animal, we must suppose that they 
have no significance. The author points out that if it does not matter 
whether the nuclear material of a cell is united into one nucleus or 
divided into two or several vacuoles, it will follow that the ordinary 
simple tJ nucleus ” is neither morphologically nor physiologically an 
entity, but is, so to speak, only a common house for a number of equi- 
valent, mutually independent constituents, which are just as well able to 
exercise their functions separately as together. These independent parts 
are the chromosomes. The other characters of the nuclei may exhibit 
considerable variations. There are cases in which the paternal chromo- 
somes (e. g. in Tiara) arise directly from the homogeneous chromatin- 
body of the spermatozoon, and others in which a resting nucleus is 
first developed from the elements of the sperm-head. It is therefore 
certain that the paternal chromatin, as it is introduced into the egg, 
is not always at the same stage of development, and this explains certain 
differences that have been observed in the relative maturity of fertilized 
ova and of the fertilizing element. The paternal chromosomes which 
are given off from the sperm-nucleus to form the first cleavage-spindle 
agree in number, size, form, and apparent structure with the maternal 
elements supplied by the egg-nucleus. 
IH. Numerical Belations of Chromosomes. — For every species the 
number of chromosomes is constant, that is, there are the same number 
in the karyokinetic figures of homologous cells. There are, however, 
the most marked differences between the homologous cells of different, 
