468 Sargant . — The Formation of the 
of development. Segmentation takes place just as in the 
second karyokinesis. The chromosomes are at first twisted, 
but become straighter and arrange themselves in the usual 
way so as to mask the spindle (cf. upper nucleus in Figs. 39, 
40). Longitudinal fission of each chromosome appears about 
the time that the nuclear plate is formed, and separation of 
the segments follows according to the vegetative type (Figs. 
42, 43). Occasionally a chromosome is found in which separa- 
tion has begun near the middle, but this is not so common as 
during the corresponding period of the second karyokinesis. 
As usual, only a small proportion of the whole number of 
preparations have spindle figures sufficiently clear and perfect 
for satisfactory counting of the chromosomes. And as I have 
not so many preparations of the third nuclear division in the 
embryo-sac as of the two previous ones, the whole number of 
countings is not so great. One spindle figure of each micro- 
pylar nucleus shows twelve chromosomes quite clearly. In 
seven other cases there are about twelve chromosomes in the 
nuclear plate of each. Among twelve comparatively clear 
chalazal spindles, five have about twenty-four chromosomes, and 
seven a larger number, not exceeding thirty-four in any case. 
Reconstruction of the daughter nuclei proceeds as after 
previous divisions. Four nuclei are in a group near the 
micropyle, four at the chalazal end. One of the micropylar 
group is the nucleus of the ovum. With its formation the 
study of the oogenetic nuclear divisions ends. 
Conclusions. 
As regards the main object of this investigation the con- 
clusion is clear. The chromosomes are divided longitudinally 
during each of the three nuclear divisions which precede the 
formation of the ovum. The first of these divisions does in 
fact differ considerably from the other two, which follow the 
vegetative type of karyokinesis, but this difference cannot be 
interpreted as concealing a transverse fission of the chromo- 
somes. I am at a loss to explain the meaning of this 
