78 THE PHYLOGENY OF THE GENUS BRACHIOMONAS 
delimited from the central green mass (FIG. 8), while in other 
cases the green and colorless regions merge into one another 
almost imperceptibly (Fic. 1). The chromatophore is here 
certainly less definitely or constantly organized than in most 
species of Chlamydomonas; in fact it would perhaps be more 
accurate not to speak of a definite chromatophore but merely of 
cytoplasm with chlorophyll more or less diffused through it. 
This variability in the extent of the distribution of the chlorophyll 
in the protoplasm is very similar to the condition in Hydro- 
dictyon, to which Harper (5, p. 179) has called attention. West 
(12) states that in his specimens of B. submarina the chroma- 
tophore never extended into the arms. This was undoubtedly 
due to the fact that he never saw his material when freshly 
collected, but only after it had been sent from near the mouth 
of the Thames to Birmingham. I find that very generally in 
freshly collected specimens the chromatophore fills the arms 
and posterior horn, but often retracts from them soon after 
being subjected to the less favorable light and aeration conditions 
of captivity. 
Imbedded in the chromatophore in a subparietal position, 
regularly on the side next to the stigma, is a single relatively 
large pyrenoid; in vigorous young specimens this is generally 
situated in front of the middle of the cell; often in older individ- 
uals it becomes posterior in position. The conspicuous red 
eye-spot is linear in form; or, sometimes at least, it may be very 
narrowly wedge-shaped, pointed in front and broader behind; 
it lies in the depression midway between two arms. Most 
frequently when the cell is at rest the pyrenoid and stigma lie 
in a median ventral position (F1G. 6). On the other side of the 
cell from the pyrenoid the nucleus may sometimes be detected 
without staining, lying in a colorless mass of cytoplasm, best 
seen in polar view (Fic. 13). When the pyrenoid lies in its © 
characteristic anterior position the nucleus is likely to be some- 
what posterior (Fics. 15, 17); if the pyrenoid becomes posterior 
the nucleus is then more often median in position. In older 
stages vacuoles often develop in the chromatophore (FIG. 4) 
as described by West (12) 
In hanging drop cultures, or in jars kept for some time in 
the laboratory, many individuals may be found which show little 
or no trace of the four lateral arms (Fics. 14, 15). Bohlin has 
shown such a form in one dividing individual. The cell wall is 
of so firm a character that it is difficult to imagine how the arms 
