580 L. DONCASTER. 
(3) In all the species the egg-nucleus at once sinks into 
the yolk and travels for some distance toward the anterior 
end of the egg; it then begins to divide, and gives rise to 
the segmentation nuclei scattered in the yolk. At the same 
time the outermost polar nucleus usually becomes flattened 
against the edge of the egg, and in all cases degenerates 
more or less rapidly. 
(4) The fate of the two inner polar nuclei varies in different 
cases. In the species which produce males from virgin eggs 
they lie from the first near together, and rapidly approach 
one another until they come into contact. The extent to which 
fusion takes place seems to vary in different species, but in 
all cases the nuclear membrane disappears, and they break 
up into chromosomes. ‘The chromosomes may form a single 
group, which contains twice as many as are found in the 
polar spindles, or when the fusion has been less complete 
two groups may be found, lying very close together and each 
consisting of the same number as occurs at each end of the 
spindle. 
(5) In the species in which virgin eggs yield females the 
inner polar nuclei usually lie farther apart, and do not 
approach one another. They may all move slowly outwards 
to the edge of the egg and gradually disintegrate (P. 
luteolum) ; or this may happen to those derived from the 
first polar nucleus, while the second polar nucleus loses its 
membrane and becomes resolved into chromosomes, which 
then show the normal number. 
(6) The chromosomes derived from the polar nucleus or 
nuclei remain in the “ polar protoplasm ” for a varying length 
of time, but seem eventually to disappear. In N. ribesii, in 
which fusion of the polar nuclei takes place, they usually be- 
come separated into two groups, in one at least of which each 
chromosome may split into two, but finally they become 
scattered and are not traceablefurther. In N. pavidus and 
N. lacteus those of one group disappear early, while those 
of the other persist unchanged for a considerable time. In 
C. varus, in which only the inner polar nucleus gives rise to 
