120 SIDNEY F. HARMER. 
The youngest figured (fig. 31) shows an embryo at the very 
beginning of this stage. The figure is taken from a colony 
which measures ‘83 mm. in transverse diameter. The diameter 
of the embryo is 45, but it must be remembered, in comparing 
it with fig. 29, that it is cut transversely to its long axis. The 
embryo is now provided with a clear outer layer of nuclei. The 
preparation for fission is indicated by the tendency of the centrally 
placed nuclei to arrange themselves in groups or in regular 
series, and by the appearance of the small slits or vacuoles 
marked S in the figure. 
Fig. 35 is a longitudinal section through an older embryo, 
in which fission has definitely begun. The brown body (not 
cut in this section) is unaltered, and the embryophore still 
hangs down freely into the fertile zocecium. The embryo is 
no longer a rounded mass, but it consists of an irregular series - 
of pieces, which show clear evidence of being engaged in fission. 
The embryonic protoplasm and nuclei take up hematoxylin or 
borax carmine with great readiness; and there can be no doubt 
from their appearance that they are engaged in active growth. 
The pieces into which the embryo divides at this stage have no 
very regular arrangement; but, as will be seen from figs. 33—35, 
the embryonic fragments are at first arranged irregularly round 
a more or less definite central space. The appearance of 
figs. 31 and 83 suggests that a kind of vacuolation of the 
central part of the primary embryo takes place, and that the 
embryonic cells thereby become dissociated into a series of 
peripherally situated groups. In tracing an embryo, such as 
that shown in fig. 34, through a series of sections, the parts of 
the primary embryo, where not completely separated from one 
another, are seen to be connected in the most irregular manner. 
Sometimes they are united with one another laterally ; some- 
times an embryo is united with its vis-a-vis by a diagonal 
connection passing across the centre of the whole mass; some- 
times a piece of embryonic tissue is prolonged into several 
finger-like processes, not unlike those of the primary embryo 
of Crisia (6, pl. xxiii, fig. 11). There is, in fact, no regularity 
or definite method in the breaking up of the primary embryo 
