568 L. DONCASTER. 
reticulum, next becomes aggregated in the centre of each as 
a closely-packed mass of chromosomes, and the nuclear mem- 
brane then disappears, and the two sets of chromosomes form 
a single group (PI. 35, figs. 7, 8, 9). In the fusion of the two 
inner polar nuclei to form what Petrunkewitsch calls the 
*‘copulation-nucleus” there is no appearance of rays in the 
surrounding protoplasm, as sometimes occurs in the fusion of 
a male and female pronucleus in fertilisation ; there is simply 
the disappearance of the nuclear membrane and the mingling 
of the two groups of chromosomes. 
The stage just described is reached between two and three 
hours after the egg is laid, and the subsequent changes up to 
the seventh hour are comparatively small as far as the polar 
nuclei are concerned. ‘lhe “ copulation-nucleus ” does not 
form itself into a definite nucleus with a nuclear membrane, 
but very shortly after the chromosomes of the two polar 
nuclei have mingled with one another to form one group, a 
separation takes place, and they come to lie in two groups 
near together in the little mass of protoplasm. Each of these 
groups is seen in several sections to consist of about eight 
separate chromosomes, lying at varying distances from one 
another, but never far apart. Neither group forms a nuclear 
membrane, and sometimes the two sets lie so near together 
that the space between them is hardly visible, but in most 
cases they are separated by a definite, though small space. 
In some sections of a stage about an hour after the fusion of 
the two nuclei (i.e. at about three and a half hours) in one at 
least of the two groups of chromosomes each appears to be 
double. And when the later stages are examined (fifth and 
sixth hours) it is sometimes, but not always, found that one 
of the groups of chromosomes contains about twice as many 
as the other. In a few sections of the later stages three 
eroups of chromosomes appear lying side by side, but 
distinctly separated into three sets, and in this case each 
group appears to contain eight chromosomes (figs. 10, 11). 
It appears, therefore, that not very long after the separa- 
tion of the chromosomes of the “ copulation-nucleus” into 
