386 BULLETIN OF THE UNITED STATES FISH COMMISSION. 
existence. In some cases two chloroplasts are distinguishable in very young cells (fig. x11, 9). 
In the liberation of the zoospores the membrane becomes to a certain extent dissolved, then the 
zoospores by their motion gradually expand the cell until finally the wall gives way and the spores 
escape. The time required for this process varies from 1 to 30 minutes. 
When the nourishment of the medium in which the organism grows becomes exhausted. the cells 
pass into a resting stage (fig. xu, 10, 11), the contents assume a yellow color, and the membrane 
becomes thick. The red globule still remains prominent. In this condition the alga can withstand 
being dried, but it quickly changes to the vegetative form when fresh nutritive solution is added. 
It was cultivated under many different conditions, but it was constant in all. 
Chlorosphera lacustris Snow, new species. 
Chlorosphera lacustris resembles somewhat the Chlorosphera angulosa Klebs, but is distin- 
guished from it in a number of details, the principal one being the size, the largest cells of this 
species measuring 9 to 10.5 4, while those of Chlorosphera angulosa measure from 15 to 30 /. 
The shape of the single cell of Chlorosphera lacustris is either spherical, oval, or ellipsoidal 
(fig. xIv,1). Asin other species of Chlorosphera, a vegetative division of the cells occurs in three 
directions of space, involving both contents and membrane, after which the cells usually remain 
connected, forming complexes of two, four, eight, or more cells (fig. xiv, 2, 3). In time these 
complexes may fall apart and the cells become spherical, as before division. 
The membrane is thin and is composed of cellulose, as the test with iodine and sulphuric acid 
shows. The chloroplast lies close to the membrane and is of the same shape as the membrane, 
though relatively much thicker. No opening through the chloroplast could with certainty be 
detected, though a lighter area at one side was prominent.* Surrounded by the chloroplast is a 
pyrenoid with a starch envelope. 
The zoospores are 6.5 to 9 long and 2.6 to 4 4 broad; they are slightly broader at the posterior 
end than at the anterior (fig. xtv, 4). Two cilia about as long as the cell are present; alsoa pigment 
spot. The chloroplast is concave and extends nearly to the anterior end. Two pulsating vacuoles 
are found just back of the cilia, and a pyrenoid is embedded in the chloroplast. Four, eight, or 
more zoospores are formed from a cell (fig. xIv,7). They are liberated by the membrane becoming 
gelatinous at one point, through which first one or two gradually force their way. The others 
follow in quick succession, leaving the empty membrane behind. On coming to rest the zoospore 
assumes at once a spherical form (fig. XIv, 5) and develops into a mature cell. In this respect it 
differs from Chlorosphera angulosa Klebs, as in that species the zoospores retain for some time 
the elongated form. They originate by the successive bipartition of the cell contents (fig. xIv, 6). 
Though both forms of reproduction, the vegetative division and the production of zoospores, 
were found in all cultures, it seemed to reproduce mainly by means of zoospores. Knop’s solution 
of 0.2 per cent concentration seemed to be the most favorable medium for development and was 
used in tracing the life history. In this solution the zoospores were formed very rapidly, and 
when transferred to distilled water they were produced in a much shorter time than is usually 
required for the production of zoospores in unicellular algee. 
Chlorosphera parvula Snow, new species. 
The present species resembles somewhat the preceding species, though, aside from being 
smaller, it is easily distinguished from it by the gelatinous nature of the membrane after division, 
causing the cells to separate slightly, though held in complexes of 2, 4, or 8 cells (fig. xv, 1, 2). 
The two species might also be distinguished by their zoospores, those of the preceding species 
being more oval or ellipsoidal than those of this species. The minute points of structure of the 
mature cell, however, the chloroplast, the composition of the membrane, and the contents of the cell, 
are the same in this species as in Chlorosphera lacustris. The diameter of the full-grown cell 
is 7.8 to 9 #. The zoospores (fig. Xv, 3), of which four are usually formed in a cell, are oval or 
spherical; when oval they measure 6.5 long and 4.5 to 5 /c broad and the spherical ones 5 to 6 /« in 
diameter. They have an obliquely placed concave chloroplast, a pigment spot, two cilia about 
1} times the length of the cell, and two contractile vacuoles. The zoospores are formed in the 
usual manner, by successive divisions of the cell contents, and are liberated by the gradual soften- 
ing of the membrane. 
