14i PROGRESS OF MICROSCOPICAL SCIENCE. 
for the most collected round tlie periphery of the cell or at its ends. 
“ Judging from the construction of the cells, and the manner of their 
multiplication, the alga before us would appear to belong to the Con- 
jugate ; but as I have not succeeded in discovering fructification in 
it, it would be rash to decide to which genus it is to be referred. 
The thread-like rows of connected cells agree with the Zygnemacece ; 
whereas, on the other hand, an unmistakable similitude to the Desmi- 
diacece , especially Cylinclrocystis, and the nearly-related genera, is 
indicated by the strongly-marked divisions into multiples of two, and 
by the tendency of the rows of cells to fall asunder, as far as the 
destructibility of the uniting cell-membranes permits, into parts con- 
sisting of cells united in pairs, which however is seldom possible, in 
consequence of the greater energy possessed by the power of multiply- 
ing the cells. As the above-mentioned small single cells, which occur 
in great numbers, are much less in diameter than those cells which 
arise from the bisection of the threads, they have perhaps a different 
origin from these latter, although the researches which I have hitherto 
been enabled to devote to this subject have not furnished any illus- 
tration of it. Were these daughter-cells arising from the division of 
the sporae, if the above-mentioned supposition with respect to the 
systematic place of the species be correct, the stadium of copulation 
or sporce, in some period of its development, ought to be found. Two 
rare forms of peculiarly constructed cells perhaps ought not to be 
passed over in silence. I have sometimes found the extreme cell in a 
thread considerably more swelled than the others, more elliptic in 
form, also provided with a thicker membrane, and with the contents 
of the cell more coarse-grained. I once found one of the middle cells 
in a thread thus transformed, and on two occasions I have met with 
single cells of the same kind. I also once met with a cell of very 
peculiar construction. It had the usual form, but was unusually large, 
with a long mass of chlorophyll, as usual, in the midst, and the 
granular matter grouped rather towards the ends of the cell. In it 
were found about twenty larger or smaller spherical bodies. Four 
of these lay arranged at each end of the cell, and were almost entirely 
opaque, of a dark brown colour, and in appearance much resembled 
the smaller cells of Protococcus nivalis. The others were translucent, 
with sharply-defined contours. As our knowledge of the nature of 
these bodies is confined to what is here stated, the fuller explanation 
of their significance must be reserved for a future investigation. In 
places similar to those in which this species occurs, and often in com- 
pany with it, Protococcus nivalis was met with. Amidst the fine 
gravel upon the ice, but to a trifling amount, small green cells are 
found, sometimes united in little groups, sometimes isolated, which 
appeared to belong to Protococcus vulgaris. Scytomena gracile, on the 
other hand, is everywhere met with in great profusion, wherever the 
gravel either lies in thinly-scattered grains on the surface of the ice 
or forms more or less thick layers. The threads lie either alone, or 
united in small bunches, as they join together at the lower part, and 
bend backwards higher up. They are pretty stiff, S-shaped, or form- 
ing a curve of several undulations, and yellowish brown in colour. 
Their length is very various, their breadth generally about 0*009 mm.” 
