( 33 ) 
Observations on Cosmarium Margaritiferum and other Des- 
MiDE^. By Mrs. Herbert Thomas, Bristol. Communi- 
cated by Dr. Carpenter. 
(Read January 24th, 1855.) 
In the month of February, 1851, while watching, for the first 
time, in the Zygnema, the curious phenomenon of conjugation, 
my attention was attracted by a beautiful object passing with 
a slow, unsteady motion over the field of the microscope ; at 
the same time I observed that in its interior small granules 
were moving with extreme rapidity, resembling a swarm of 
bees more than any other object to which I can compare it. 
This plant I afterwards knew to be Cosmarium margaritife- 
rum. From that period I have made this plant the object of 
my constant observation, and have at the time recorded by 
delineation anything which struck me as new, without, how- 
ever, endeavouring to draw conclusions from my observations, 
which, from my imperfect microscopic knowledge, I knew 
might too often prove incorrect. 
The plant, as I first saw it in February 1851, is figured at 
Plate v., fig. 3. In each half, the centre was occupied by a 
vesicle (as it appeared) filled with moving granules, while 
smaller vesicles were at the four sides. The granules did not 
appear to circulate through the plant, but kept to their own 
place, which was either a bag or cavity, 1 could not decide 
which. In fig. 1, subsequently drawn, I have recorded that 
the granules were swarming over the whole plant. This may 
possibly have been due to alteration of focus, bringing the 
larger granules more prominently into sight ; or it may have 
arisen from some difference in the early growth of the plant, 
as the specimens represented in figs. 8 and 9 showed corre- 
sponding differences, fig. 8 developing into fig. 1, fig. 9 
into fig. 3. 
1 now carefully preserved the water in which my Cosma- 
rium was tolerably abundant ; and by continually changing 
it, kept the plants healthy. From my recollection of certain 
bodies which I have since occasionally seen, I think that con- 
jugation may have taken place during the summer ; but I was 
not then acquainted with the sporangia of the Desmidiae. 
As the summer advanced, many of the plants lost their spring 
beauty and active motion ; fig. 10 represents the appearance 
of some ; in others the inner membrane was very much shrunk, 
containing only a little of the green matter, or if in active 
life, the colours assumed more of an autumn aspect, probably 
from the colour of the light thrown upon them. In fig. 6 
VOL. III. d 
