228 Hazen: Lire History oF SPHAERELLA LACUSTRIS 
name “ primordial cell.” Taking into account the radial strands 
of protoplasm and the network which they probably form, this 
term is hardly suitable. The protoplasmic mass must be re- 
garded as the single chromatophore (Vines, '86, Bütschli, '84). 
This chromatophore, at first solid, may in the later stages become 
vacuolated so as to present the form of a hollow green sphere in- 
closing the red nuclear globule (Fig. 30). Frequently the chloro- 
phyl of this hollow shell becomes reduced in places so that it ap- 
pears to be pierced with holes (Fig. 15). It is such conditions 
which have given rise to the statement that the zooids contain sev- 
eral chromatophores. 
The extent to which the haematochrom is changed into chlo- 
rophyl appears to depend on the conditions which ordinarily affect 
the production of chlorophyl. The zooids do not need the haema- 
tochrom but much of it may be retained for a day or two if the 
temperature is not favorable for the formation of chlorophyl. 
Light is apparently not so essential a factor as warmth, for zooids 
kept in the dark may develop considerable chlorophyl Under 
such circumstances it is noticeable that the haematochrom is more 
scattered and mixed with the chlorophyl, but when these zooids 
are brought into the light the haematochrom soon becomes col- 
lected into a central globule. 
When the conditions are favorable for the formation of chlo- 
rophyl the haematochrom may disappear altogether in the later 
stages (Fig. 32) ; it never seems to have the character of the red 
“ eye-spot" of other genera, but gradually fades out. 
In the green chromatophore are embedded several (4-8 
pyrenoids. These were called Chlorophylltlischen by Cohn (' 50), 
who expressed doubt as to the presence of starch in this alga. 
Braun ('51) recognized their true nature in relation to starch for- 
mation. Frequently the presence of starch cannot be demonstrated 
by application of iodin, but the test is successful if the culture has 
been furnished with sufficient light and aération. The pyrenoids 
are especially prominent after freezing ; they then show a clear 
nuclear spot in the center. 
