240 Rickett. — Fertilization, of Sphaerocarpos . 
of two apparent chromosomes may really be two whose ends are close 
together. The X-chromosome is plainly visible, also, close by it, the 
Y-chromosome. Fig. 22 shows the spindle very plainly, but the chromo¬ 
somes are too close together to be counted. Even here, however, the X- 
and Y-chromosomes are evident, close together as in the case just described. 
There seems no doubt that dividing nuclei of the embryo contain the full 
sporophytic number of chromosomes (16). For comparison with these 
sporophytic groups I have included figures of division stages from cells of 
the wall of the venter. Fig. 23 shows an equatorial plate; the chromosomes 
(except the X-chromosome) seem to be cut in cross-section ; eight of them 
are visible, seven being small rounded bodies, and the much longer and 
thicker X-chromosome extending up and down the spindle. Fig. 24 shows 
an anaphase, in which eight daughter chromosomes 
are moving towards each pole of the spindle. In 
several cases the two daughter chromosomes of 
a pair are still attached to each other at one 
end. Here also the X-chromosome is easily dis¬ 
tinguished. 
Ninth Phase. 
This phase includes embryos which have 
undergone two cell divisions. The four cells are 
in all cases that I have observed arranged in 
a row, as illustrated in Text-fig. 3. This account 
agrees with that of Campbell ( 1918 ), but is contrary 
to the description of Cavers ( 1911 ), who says that 
the ‘ embryogeny is of the Marchantiales type ’— 
that is, the young embryo passes through an octant 
stage. Some unpublished work of Miss E. M. 
Ritchie indicates that there is some variation in the plane of the second 
division in the embryo of Sphaerocarpos. All the cells are of approxi¬ 
mately the same size, and do not differ essentially in appearance from those 
formed by the first division, except that the cytoplasm is apparently alveolar 
in structure, and shows only slight traces of the dense material that sur¬ 
rounded the egg nucleus during Phases 5 and 6. 
Tenth Phase. 
This phase is merely a convenient grouping of all stages that were 
observed subsequent to those already described. The embryo has become 
a mass of cells, a longitudinal division having occurred in some cells. Since 
the present paper is concerned only with fertilization, no further discussion 
of embryological development will be included. 
Text-fig. 3. Arche- 
gonium containing a four- 
celled embryo. Eighty-four 
hours after flooding, x 320. 
