MATURATION AND FECUNDATION OF THE OVUM. 121 
is bilaterally symmetrical : two of its branches which meet at 
an obtuse angle are similar to one another, the third is dis- 
similar. The plane of symmetry passes through the axis of 
this third branch. 
At the outer pole of each of the similar branches is a large 
group of granules. The form of the whole group is somewhat 
hemispherical, the flat base being towards the branch. From 
the hemisphere pass outwards a few diverging radii of monili- 
form protoplasm, part of the protoplasmic reticulum of the 
ovum. The fibrils of each branch arise from the base of 
the hemispherical group of granules ; some of these fibrils are 
regular in thickness, some present varicosities, some are moni- 
liform. Two or three fibrils in each branch are conspicuous by 
their greater thickness, they lie near the axis of the branch and 
are inserted into the chromatic globules. The other fibrils are 
curved, and change direction when they reach a clear spherical 
body, in the centre of which the chromatic globules are placed. 
The axial fibrils penetrate the spherical body. The fibrils which 
are near the vertical branch of the Y meet in acute angles and in- 
terlace, and in this way the vertical branch is formed. The ver- 
tical branch is not columnar but flattened in a plane perpendi- 
cular to the line uniting the two poles of the similar branches. 
Another illustration which the author employs to facilitate the 
conception of the figure is that of the toy known as cup-and-ball. 
The stem of the cup is formed by the vertical branch of the Y, 
the ball is the clear spherical body containing the chromatic 
globules, while at opposite points the cup runs out into two 
poles : it must be remembered that the stem of the cup is flat, 
not round. The limits of the clear spherical body become less 
distinct as development advances. Usually in optical section 
there are two groups of chromatic globules, one on either side 
of the plane of symmetry ; each group shows two globules but 
really contains four. Outside the figure in each of the angles 
between the vertical branch and the superior branches is a 
mass of deuteroplasmic vitelline substance limited externally 
by a convex surface (see fig. 4, PI. X). 
