Notes on British Flagellates. I — IV. 343 
of action and cause a uniform and fairly rapid forward movement 
combined with the customary rotation of the organism upon its own 
axis. I have been unable to observe any change of shape on the part 
of the protoplast, either in the free-swimming or resting individual. 
There is a single chloroplast which is almost completely 
spherical possessing only a small opening at the anterior end, placed so 
as to face between the cilial apertures of the envelope (Fig. 1, D). 
In most cases the chloroplast appears minutely granular, but in some 
individuals it seemed to be more or less fissured, especially at the 
anterior end, without however actually breaking up into segments; 
starved specimens which had been kept in darkness for some days 
exhibited reticulation of the chloroplast, the actual substance being 
interrupted by oval or circular meshes. The chloroplast occupies 
practically the whole of the body, leaving only a slight colourless 
three-cornered or rounded area at the front end beneath the cilial 
beak (Fig. I, C). The product of assimilation is starch, healthy 
individuals becoming almost uniformly bluish-black on staining 
with Iodine. Even after some days’ sojourn in darkness a number 
of large spherical or oval bodies which become stained a dark colour 
with Iodine are still distinctly recognisable in the cell-contents ; 
there are from five to eight of these bodies which appear to lie on the 
inner face of the chloroplast and for the most part nearer the front 
than the back end of the cell, but apart from that, exhibit no 
regular orientation (Fig. 1, C, F). In view of their persistent 
character and large size these structures are probably to be regarded 
as pyrenoids, with a closely fitting sheath of very minute starch-grains. 
The small nucleus appears in all cases to occupy a central 
position (Fig. 1, A, B), being clearly seen through the opening of 
the chloroplast in individuals viewed from the front end (Fig. 1, G). 
The nucleus is generally quite easily visible in the living organism, 
but shows up very plainly after staining with safranin. A prominent 
eye-spot, of an elongated oval shape and appearing as a slight 
elevation on the periplast, is situated on one side a little way from 
the front end of the cell (Fig. 1, A, C, G). I have been unable to 
observe any contractile vacuoles. 
It appears probable that there is an actual space between the 
envelope and the contained cell, since individuals placed in 
salt-solution or alcohol exhibit marked contraction of the proto¬ 
plast resulting merely in a widening of the space between the 
latter and the envelope ; in very rare cases, however, the contracting 
protoplasm brought to light a second boundary line internal to the 
envelope, as though there had been some substance, such as mucilage, 
