508 
L. DONCASTEK AND J. GRAY. 
take place until both nuclei are fully formed and contain * 
visible chromosomes. It is doubtful, however, whether this t 
can be the complete explanation of the vesicle-formation, for 
without further qualification it does not provide a reason for 
the production of vesicles in the second segmentation division. 
That the vesicle-formation is a phenomenon depending on the 
disturbance of the osmotic relations between the chromosomes 
and cytoplasm seems nevertheless a hypothesis which should 
be taken into account. 
EXPLANATION OF PLATES 28 axd 29, 
Illustrating Mr. L. Doncaster and Mr. J. Gray’s “ Cytological 
Observations on the Early Stages of Segmentation of 
Echinus hybrids.” 
[The figures were drawn with a Zeiss apochroinat. 3 umi.. n.a. ITO and 
with coinpens. o.c. 12. They are not all drawn to the same scale, figs. 
5, 13, 14, 20, 22, 23, 29, 30 being on a smaller scale, figs. 8 and 17 on a 
larger scale than the rest. Since the chromosomes on the spindles are 
at different levels in the section, it was found that drawing Ijy eye 
was preferable to using a camera. In some cases where the cell 1 
outlines are drawn, the nuclei or spindles are enlarged i-elatively to the I 
cell.] ' f 
PLATE 28. .' 
Fig. 1, o, b. — E. acc\tus ? X (J. Two anaphase groiqis in face, 
from different eggs, 38 chromosomes in each. The two chromosomes 
outside the group to the left in 1 belong to the other end of the 
spindle. 
Fig. 2, a, b. — E. esculentus ? X (J. Two anaphase groujis in 
face, from the same spindle. Thirty-eight chromosomes in 1 b. 37 or 
38 in 1 a. 
Fig. 3, «, — E. esculentus $ X Anaphase (second division) ; 
spindle seen sideways. 3 a and 3 b are from successive sections ; 38 at 
each end. 
Fig. 4. — Esculentus $ X acutus J'. Anaphase, second division, 
in face ; 38 chromosomes. 
Fig. 5. — Esculentus ? X acutus . Anaphase, second division, 
side view'. 
I 
