THE PHYLOGENY OF THE GENUS BRACHIOMONAS 87 
hanging drop cultures showed almost a lattice-like appearance 
of the chromatophore. Although the chromatophore is hollowed 
out about as far as the middle of the cell, or sometimes even 
more deeply, nevertheless the position of the nucleus is notably 
less central than might be expected, for it lies approximately 
in the anterior third of the cell. 
A point of considerable interest is the position of the stigma 
and contractile vacuoles. Regularly the eye-spot is so placed 
that when the cilia are stretched out in a plane parallel to the 
stage of the microscope the stigma lies on the apparent right 
side of the cell and in a slightly upper focus, or with the cell 
revolved 180° the stigma lies on the apparent left side and at a 
slightly lower focus; in such a position only one of the small 
contractile vacuoles is visible. If the cell is revolved only 90° 
from the first position, so that one of the cilia lies nearer the 
observer and the other at a somewhat lower focus, the stigma 
shows its disc-like shape in an upper central focus (FIG. 48) 
‘ and the two contractile vacuoles may be seen side by side at 
the same time, though one is always smaller than the other, 
on account of the alternation in their pulsations. This position 
of the stigma and cilia in one plane and the contractile vacuoles 
in another plane perpendicular to it indicates a dorsi-ventral 
character of the cell which appears to me to be the rule in many 
species of Chlamydomonas, though it seems to have received 
little or no attention from students of the group.* 
The dorsiventral differentiation in Brachiomonas, as men- 
tioned above and indicated in Fics. 6, 7, 13, 15, and 32, is 
slightly different; there the cilia normally stretch out in a plane 
perpendicular to that which passes through the stigma, pyrenoid, 
and nucleus, and most commonly the zoospore comes to rest 
with the stigma lying exactly in the middle on the ventral side, 
or (less often) on the dorsal side, toward the observer. In 
many of the figures which seem to indicate a different relative 
position of the eye-spot and cilia, the latter were actually lying 
in a plane oblique to that of the microscope stage, which could 
not easily be shown in the drawings. 
* There are, it is true, many published figures of Chlamydomonas which 
show the two contractile vacuoles side by side apparently in the same plane 
with the cilia; but in cells exhibiting so much movement it is very easy to 
transfer what is seen in one view to a sketch representing in general a different 
view, unless one is keenly on the lookout for such a point. Probably also 
many of our somewhat classic figures are not made from camera lucida draw- 
ings of quiescent individuals, as they should be to determine such features. 
